itochondrial activity and cell composition

itochondrial activity and cell composition

volution of mammalian endothermic metabolism:
itochondrial activity and cell composition
A. J. HULBERT AND PAUL LEWIS ELSE
Department of Biology, University of Wollongong, Wollongong, New South Wales 2500, Australia
ulbert A. J., and Paul Lewis Else. Evolution of mamm endothermic metabolism: mitochondrial activity and cell
KTo-n< & »?«hysioL 256 (Re^latory Integrative Comp
v-ompared
1 ^ ?63f6
Vf ?-B0dy vitticeps
C0raP°si^n
was measured
in Amphibolous
and Rattus
norvegicus
pti e and a mammal with the same weight and body
erature). Homogenates were prepared from liver, kidney
.heart, lung, and skeletal (gastrocnemius) muscle, and
:hondria were isolated. Cytochrome oxidase activities of
tlssu* h°m ogenates and isolated mitochondria were measnrif v Wa* ?5?tem content. Phospholipids were
£r?m
J1™ MJ?
bdnev'liver,
andkidney,
^e fattyheart,
acid composition
letermined.
The brain,
and skeletal
te were significantly larger in the mammal, whereas the
reproductive organs, lung, and digestive tract showed no
Sd WT™
SiZG-A11
tissues
examined
ined
-o0%m
more
proteinmammaIian
and phospholipid
than
the reve reptilian tissue. Although the mammalian phosphocontained significantly less total unsaturated fatty acids
unsaturated fatty acids were significantly more polyun■ted than in the reptilian tissues. Tissue cytochrome'oxiictivity was significantly greater in mammals when exd on a wet weight basis but not when expressed on a
protein basis. Mitochondrial cytochrome oxidase activitv
protein basis) was the same in both species in liver"
.and brain but in heart, lung, and skeletal muscle
lllmTK °ndf-ia
W6re twke
as active
as rePtiHan
•onona.
The implications
of these
differences
in tissue
=iuon were discussed relative to the evolution of mamendothermy.
consumption; ectothermy; endothermy; reptiles; phosds; membrane fatty acids; tissue protein; cytochrome
ate are its body size, its body temperature, and
Tit is an endotherm or an ectotherm. Many
have shown that resting endotherms (mammals
•as) have a level of metabolism that is approxifour to fve times that of similar sized ectotherms
Tther
V6'1,8)>. ThlSparameters
difference such
is also
manifest
physiological
as maximal
ac rate, growth rate, and aerobic endurance are
ed oetween the two groups (3, 4). Over the last
as the mammal and the central netted dragon (Amphi
bolous nuchalis) as the reptile (8, 19); however, later
when it became necessary to prepare isolated liver cells
we changed the comparison to that between the lar-er
rat {Rattus norvegicus) and the bearded dragon (A. vit
ticeps) (12). In both of these comparisons the reptile is
the same size as the mammal and has a preferred body
emperature that is the same as the mammal's body
temperature. These two comparisons have given almost
identical results, and we believe they offer an excellent
system for understanding the cellular basis of endoth
ermy and its associated thermogenesis.
The initial comparison was restricted to four tissues
Oiver, kirJxiey heart, and brain) and showed that the
mammal had larger internal organs, which contained
more mitochondria, and that the total mitochondrial
membrane surface area of these tissues was approxi
mately fourfold greater in the endotherm than the ec
totherm (8). This was later shown to be a general differ
ence between mammals and reptiles and that mitochon
drial membrane surface area was allometrically related
to body size with a similar exponent to the metabolic
rate-body size relationship (10,11). More recently, it has
been shown that the mammalian liver and kidney are
considerably leakier" to sodium and potassium ions
than the corresponding reptilian tissues, and this greater
leakiness possibly explains in part the increased Oo
consumption ofthe mammalian tissues (12). The present
paper extends the detailed comparison of the two lar-er
species and is concerned with two main questions: 1) do
mitochondria from mammalian tissues have similar enzymic activity to those from reptilian tissues; and 2) was
the increase m metabolism during the evolution of mam
malian endothermy associated with any major changes
in the composition of tissues?
MATERIALS AND METHODS
y\e1her)iaNN wZ$' ^"l ^-bi^-aminoethcchrome
h r o m pc (horse
r f * f fheart),
f a d dlecithin
( E G TA
) ' sIX-E,
a l t - f egg
^ e cyolk)
yto
(type
Mcorhcaci^
(BHtT SiH r(HfES)'.^^ hydroxy toW
InTk i CIC 3Cld' and reference fatty acid
*££ Tn Tk6 0bttned fr0m the Si^a Chemical.
f r^^f^?.^?- V; BSA) was obtained
0363-6119/89 $1.50 Copyright © 1989 the American Physiological Sc
ethyl ether were from Mai-
ENDOTHERMY AND CELL COMPOSITION
1. Comparison of body composition of reptile
wlurus vitticeps and mammal Rattus norvegicus
weight, g
dy weight
an
er
Iney
art
>mach
estines
ng
productive
in + fur
eletal muscle
tier + skeleton
TABLE 2. Comparison of protein content of tissues
from reptile Amphibolous vitticeps
and mammal Rattus norvegicus
Significance
of Differenc
A. vitticeps
%
.
R. norvegicus
9
304±34
10
310±24
NS
0.13±0.01
2.84±0.42
0.41±0.04
0.29±0.01
1.12±0.01
1.51±0.10
0.81±0.04
0.66±0.13
21.21±1.28
34.58±1.94
36.42±1.43
0.69±0.04
4.21±0.11
0.89±0.04
0.40±0.01
0.49±0.03
2.04±0.15
0.68±0.05
1.37±0.31
20.00±0.55
42.82±0.90
25.94±1.25
P < 0.01
P < 0.01
P < 0.01
P < 0.01
P < 0.01
P < 0.02
NS
NS
NS
P < 0.01
P < 0.01
s are means ± SE measured as percent of body weight (minus
stomach contents); n, No. of animals. NS, not significant.
n
Body weight, g
Protein content,
mg protein/g tissue
Kidney
Heart
Lung
Skeletal muscle
A. vitticeps
R. norvegicus
Significance
of Difference
6
340±43
6
321±33
NS
90±10
91±5
53±3
85±4
60±5
81±6
165±5
126±7
105±1
114±5
90±7
120±12
P < 0.01
P < 0.01
P < 0.01
P < 0.01
P < 0.01
P < 0.02
Values are means ± SE measured as mg protein/g tissue, n, no. of
animals.
TABLE 3. Comparison of phospholipid fatty acid
composition of liver from reptile Amphibolous
vitticeps and mammal Rattus norvegicus
Kile and 6.2% in the mammal. The mammal also
jjnificantly more skeletal muscle than the reptile,
Significance
ere was no significant difference between the two
A. vitticeps R. norvegicus of
Difference
3 in the proportion of body mass devoted to body
5
5
rig, the lungs, and the reproductive system. The n
P < 0.05
0.53±0.09 0.86±0.07
Dtal of these differences (10.9% of body weight) Phospholipid content,
mg/g tissue
•mpensated by a significantly greater "other" com- Fatty acid composition,
t. This other component is primarily the skeleton,
mol %
0.8±0.3
P < 0.05
is a much larger part of the reptile than the
1.8±0.2
X,
16.5±2.3
NS
14.8±1.6
16:0
lal.
0.3±0.1
NS
1.3±0.5
16:1
lough the intestines were significantly larger in the
0.6±0.1
NS
0.6±0.1
17:0
lal, the stomach was significantly smaller than in
0.5±0.3
NS
0.7±0.1
Xa
27.1±3.0
NS
20.2±1.3
ptile, and the net result was that there was no
18:0
5.3±1.4
NS
12.6±2.7
mce in the portion of body mass devoted to the
18:1"
2.2±0.2
NS
3.0±0.9
18:lt
ive system between the mammal and the reptile.
8.2±0.2
NS
20.7±5.8
18:2
of these differences are compatible with the much
0.1±0.1
NS
2.2±0.9
18:3
■ level of energy metabolism in the endothermic
30.6±1.0
P < 0.001
20:4
13.7±2.0
0.3±0.1
P < 0.01
ial compared with the ectothermic reptile. The lack
2.2±0.4
20:5
0.7±0.1
NS
1.0±0.2
22:4
erence in the digestive system at first seems unP < 0.01
2.1±0.1
1.3±0.2
22:5
The mammalian system is the more rapid digestor
P < 0.05
1.5±0.3
4.3±0.9
22:6
)sorber of nutrients, and the relatively small stom- ^Unsaturated
P < 0.005
61.1±1.2
53.7±1.1
fatty acids
the mammal is probably correlated with its more Unsaturation index
P < 0.01
155±4
185±8
P < 0.05
18.0±0.1
18.4±0.1
nt mastication of food in the mouth before swal- Average chain length
P < 0.001
1.02±0.35
3.76±0.17
20:4/18:2
'. The physiological and structural digestive adaps associated with the evolution of endothermy in
Values are means ± SE; n, no. of animals. Only fatty acids that
lals are excellently covered in a series of papers by constituted >0.5% of total are shown. First no. represents no. of carbon
atoms, whereas second represents no. of double bonds. Xi and X2 are
ov and co-workers (20, 21).
unidentified fatty acids. 18:1* is oleic acid, whereas 18:1+ is cis vacenic
the mammalian tissues examined had significantly acid. Unsaturation index is sum of (mol % x no. of double bonds) for
protein than the corresponding reptilian tissues each fatty acid. Average chain length is sum of (mol % X no. of carbons/
j 2). The difference was remarkably consistent 100) for each fatty acid.
en tissues, with the mammalian tissue having on
>e 58% more protein than the same amount of lipid content presumably represents a greater amount of
an tissue. As well as having a greater protein membranes in the mammalian tissue compared with the
it, mammalian tissues also contained a signifi- reptilian tissues. The difference in protein content, while
• greater amount of phospholipids (Tables 3 and 4). including the effect of more membranes (and thus more
)holipid content was compared in liver and kidney membrane proteins) in mammals, would seem to be
out in both these tissues there was on average 54% predominantly a reflection of the larger amount of nonphospholipid in the tissue from the mammal than membrane protein in the mammal compared with the
: tissue from the reptile. This value is very similar reptile.
Tables 3 and 4 also contain an analysis of the fatty
i protein difference, and both are related to the
r metabolic rate of the endothermic mammal com- acids that make up the phospholipids in liver and kidney
with the ectothermic reptile. The higher phospho- tissues from the mammal and reptile. One interesting
ENDOTHERMY AND CELL COMPOSITION
TABLE 4. Comparison of phospholipid fatty acid
composition of kidney from reptile Amphibolous
vitticeps and mammal Rattus norvegicus
Significance
A. vitticeps R. norvegicus of Difference
Phospholipid content,
mg/g tissue
Fatty acid composition,
mol%
X,
16:0
X,
o
0.54±0.02
0.79±0.06 P < 0.005
2.4±0.6
11.5±0.7
1.6±0.6
0.4±0.1
1.0±0.4
20.5±0.4
14.0±3.5
3.6±1.0
16.5±3.4
3.2±1.6
13.0±1.3
2.4±0.5
1.1±0.3
2.5±0.6
1.8±0.5
61.6±1.7
159±5
18.0±0.2
1.02±0.28
1.2±0.4
16.2±1.7
0.5±0.1
0.6±0.1
0.9±0.3
25.3±3.2
6.3±1.5
2.2±0.2
7.7±0.3
0.1±0.1
30.7±0.5
0.5±0.1
0.9±0.1
1.2+0.2
3.5±0.7
53.9±0.8
183±3
18.4±0.1
4.04±0.24
NS
P < 0.05
NS
NS
NS
NS
NS
NS
NS
NS
P< 0.001
P < 0.01
NS
P < 0.01
P < 0.05
P < 0.005
P < 0.005
NS
P< 0.001
18:0
18:1*
18:1+
18:2
18:3
20:4
20:5
22:4
22:5
22:6
%Unsaturated fatty acids
Unsaturation index
Average chain length
20:4/18:2
Values are means ± SE; n, no. of animals. Only fatty acids that
constituted >0.5*rc of total are shown. First no. represents no. of carbon
atoms, whereas second represents no. of double bonds. Xi and X> are
unidentified fatty acids. 18:1* is oleic acid, whereas 18:1+ is CIS vacenic
acid. Unsaturation index is sum of (mol % x no. of double bonds) for
each fatty acid.. Average chain length is sum of (mol % x no. of carbons/
100) for each fatty acid.
Table 5 shows a comparison ofthe cytochrome oxic
activity of six tissues from the mammal and the rep
When compared on a wet weight basis, the cytochn
oxidase activity of all tissues was significantly greate
the mammal than in the reptile, however, when comp,
on a tissue protein basis, only one tissue (lung) he
significantly greater cytochrome oxidase activity in
mammal, one tissue (brain) showed a significantly
duced enzyme activity in the mammal, and all the o
tissues showed no significant difference between
mammal and the reptile. This change is consistent i
the higher protein content of the mammalian tis;
compared with the equivalent reptilian tissue, espec:
the brain (see Table 2). When isolated mitochoE
from these tissues are compared (Table 5), reptilian 1
kidney, and brain mitochondria are not significa
different from the equivalent mammalian mitochon
Both skeletal muscle and cardiac muscle mitochor.
from the mammal had very high cytochrome oxi
activities (on a per mg protein basis) that were a
twice those of the equivalent reptilian mitochon
Although the cytochrome oxidase activity of lung r
chondria was not as great as mitochondria from mi;
the total activity of the mammalian mitochondria
twice that of reptilian mitochondria.
Mammalian mitochondria tended to have a gr
protein content relative to mitochondrial lipid comp
with reptilian mitochondria, although this was onh
finding (in both species) is the remarkable similarity
between the two tissues. There were significant differ
ences between the reptile and mammal in several indi
vidual fatty acids. In general, there were less saturated
fatty acids in the mammalian phospholipids than repti
lian phospholipids, but the mammalian unsaturated fattyacids tended to be more polyunsaturated than the repti
lian fatty acids. It can be calculated that the unsaturated
fatty acids in mammalian phospholipids averaged 3.4
double bonds per molecule, whereas the corresponding
value for reptilian phospholipids was only an average 2.5
double bonds per unsaturated fatty acid molecule. This
was true for both the liver and the kidney. The net result
of this difference is that even though the percentage of
unsaturated fatty acids was significantly reduced in
mammalian phospholipids, the unsaturation index (the
average number of double bonds per 100 fatty acids) was
significantly increased in the mammalian phospholipids.
Mammalian phospholipid fatty acids were on average
slightly longer than their reptilian equivalents, although
this was not statistically significant in the kidney. These
differences were largely (but not solely) due to a reduced
amount of linoleic acid (18 : 2) in mammalian phospho
lipids and an increased content of arachidonic acid
(20: 4). The differences were statistically significant in
both tissues in the case of 20 : 4 but were not statistically
significant in the case of 18: 2. This is probably due to
the high variability of 18:2 content in the reptilian
phospholipids.
table 5. Comparison of tissue and mitochondrial
cytochrome oxidase activity in tissues from reptile
Amphibolous vitticeps and mammal Rattus norvegi^
n
Body weight, g
Tissue cytochrome oxidase
activity
nmol 03 • mg wet tissue"1 ■
min
Liver
Kidney
Brain
Heart
Lung
Skeletal muscle
nmol 02 mg pr-cein"1 •
min-1
Liver
Kidney
Brain
Heart
Lung
Skeletal muscle
Mitochondrial cytochrome
oxidase activity,
nmol 03-mg
protein-1-min-1
Liver
Kidney
Brain
Heart
Lung
Skeletal muscle
Signific
ofDiffe
A. vitticeps
<?. norvegicus
6
340±43
6
321±33
14.3±4.4
19.9±1.2
12.2±1.4
21.1±1.6
2.5±0.2
6.7±1.4
37.0±2.6
30.6±1.1
16.9±1.3
29.6±0.9
9.4±0.7
15.6±1.2
P<'
P<<
P<<
P<
P<
P<
143±32
220±16
230±24
251±22
42±3
85±22
226±20
246±11
161±15
261±12
107±9
136±17
N
N
P<
N
P<
N
NS
*■'
500±121
895±117
464±73
891±172
263±37
751±127
-.571±67
649±68
441±54
1,782±152
531±55
1,532±274
>
r-
>
P<
P<
P<
Values are means ± SE; n, no. of animals. All cytochrome
activities were measured at 37°C. NS, not significant.
ENDOTHERMY
AND
CELL
COMPOSITION
R67
P*k
(^e
i ; n eSi^if!cant
C y t O C h rin
n r n**?er
p n v i and
n a c o brain
opfuM
+ J nTable
n ; + 6).
: . - -gastrocnemius
. « — : u i - * . - • _ muscle
- . 1 » was
t . . the only skeletal muscle exinvolved and^he accuracy of the measurements,
>arison of these values should not be too rigorous,
major assumptions are that cytochrome oxidase
ity is not affected by the isolation of mitochondria
hat the protein content of the mitochondrial prep3n is both solely mitochondrial protein and contains
ally all ofthe protein originally in the mitochondria.
ming these to be true, we can see from Table 7 that,
the exception of kidney tissue, there are no signifidifferences in the proportion of cellular protein that
and in the mitochondria of the reptilian tissues
ared with the mammalian tissues. In the mammaddney, 37% of cellular protein is calculated to be
:hondrial, which is significantly greater than the
calculated for the reptilian kidney. In both species,
Dal muscle is the tissue with the smallest proportion
l t l l n r n r n t o i n O O m ^ n n l . n - J . : . l j . _ • T- v * i •
s because ofthe large amounts of contractile protein
iscle. In both species, cardiac muscle has twice the
hondrial protein (relative to total cellular protein)
does skeletal muscle. In the present study, the
•: 6. Comparison of relative protein to lipid content
ochondria from tissues of reptile Amphibolous
ps and mammal Rattus norvegicus
A. vitticeps R. norvegicus Sj^i£lcance
of Difference
eight, g
ondrial protein-to-lipid
io, mg protein/mg lipid
340±43
321±33
NS
1.0±0.2*
3.6±0.3
P < 0.02
1.9±0.2
2.2±0.5
NS
0.5±0.1
0.9±0.1
P < 0.01
2.0±0.6
1.5±0.9
NS
1.0±0.5
1.5±0.4
NS
tal muscle
0.6±0.1
1.2±0.5*
NS
3s are means ± SE; n, no. of animals. NS, not significant. * No
als = o.
sy
7. Comparison of relative mitochondrial protein
c(as % of total cellular protein) of tissues of reptile
bolurus vitticeps and mammal Rattus norvegicus
A. vitticeps R. norvegicus Si£J»ficance
of Difference
ight, g
ndrial protein,
f total
ilar protein
•
V
25±2
"il muscle
muscle
340±43
321±33
<"=:b
32±6
41±o
41±5
25±2 3 7 ± 437±4
55±8
5
5±8
39±5
39±5
33±6
3
3±6
15±1
15±1
20±6
2
0±6
21±3
21±3
13±3
7±1*
13±3
7+1*
NS
P<0.05
NS
NS
NS
NS
\is***
*_** "' n0'protein
0f animalsNS, not significant.
No.
- 5.Tex?S
Mitochondrial
was calculated
as tissue *cyto-
^dase activity x 100/mitochondrial cytochrome oxidase ac-
reptiles (11).
DISCUSSION
Previously, it has been shown that endothermic mam
mals have a greater amount of (metabolically active)
tissues than ectothermic reptiles, and, via the techniques
of quantitative electron microscopy, it was shown that
these mammalian tissues contain a greater amount of
mitochondria than the same reptilian tissue (8, 11).
When all factors are taken into account, endothermic
mammals average a total mitochondrial membrane sur
face area that is four to five times that for ectothermic
reptiles, and this difference is similar to that for their
respective standard metabolic rates (11). Such a corre
lation assumes that mitochondria from endotherms have
— — —-v*— """"ww w unuoc Hum e^Luuierms. in
the present study we have examined this assumption by
measuring the enzymic activity of isolated reptilian and
mammalian mitochondria. Cytochrome oxidase activity
was chosen because it is relatively easy to measure and
has been previously used in a number of comparisons of
tissues between ectotherms and endotherms. It is the
terminal respiratory enzyme and is responsible for the
consumption of 02.
The answer to the question posed in the introduction
is both yes and no. Mitochondria isolated from three
tissues (liver, kidney, and brain) showed similar enzymic
activity in both the endotherm and the ectotherm,
whereas mitochondria from muscle (both skeletal and
cardiac) and lung showed twice the cytochrome oxidase
activity (on a per mg mitochondrial protein basis) in the
endotherm compared with the ectotherm (see Table 5).
An analysis of previous studies from the literature gives
a similar dichotomy between tissues. Mitochondria iso
lated from the liver of a wide range of ectotherms are
very similar in their properties to those isolated from
mammalian liver (5, 28). A similar finding was made in
a comparison of brain mitochondria from a number of
vertebrates (30). In muscle, although the cytochrome
oxidase content of fish heart mitochondria is about onethird of that of beef heart mitochondria, the 02 con
sumption per mole of cytochrome oxidase is similar in
both groups (32).
Because cytochrome oxidase activity was measured as
02 consumption (when provided with excess substrate)
and the size ofthe tissues was also measured, it is possible
to calculate the total 02 consumption by cytochrome
oxidase for the summed tissues for both animals. When
this is done, the total 02 consumption by cytochrome
oxidase is 22 ml 02/min for the reptile and 63 ml 02/min
for the mammal. In both species, skeletal muscle is
responsible for 76-80% of the summed 02 consumption
by cytochrome oxidase, and both of these values are very
similar to the maximal metabolic rates expected for the
two species (11).
Akhmerov (1) has recently reported that the mito
chondria of endothermic animals are qualitatively differ-
R68
ENDOTHERMY
AND
CELL
COMPOSITION
/ nr rt>i t„ a
u it„i„v e
o n^„^A^ J
a \^ PA
T V i pft tpA a
e
e n t f r o m t h o s e f r o mm i ce catnoi m
t haei sr. m*ipcu n .wa«n* «i m*a" *l .s* .; —Q.u a
XrX
is
however ♦
since
reptilian
tissue (see
and proportionate!}
4). lhere are
ls difficult
rl 1Cv2__STS.
" JLl
unsaturated
fattyTables
acids 3 but
out previously any company u «««^-- ^ reported for a more extensive comparison
between ectotherms and endotherms should take into oeen «P° ectothermic and endothermic verfe
*""^SHS _&ttsss*_5__
QWgfltliU
ence between r
therms is interesting
chondrial membranes of endotherms maj
membrane
in the endotherm (12). The finding by Akh» . \ , i . i i . l : j — „ U « - . J - ; n c - V- i / i n t o m i i r h c r r p a t P
ference between these two tissues found in the present tissues compared with reptiliantissues^ (12, 19).
study. Although such a qualitative difference in the mi- s:
tochondria of ectotherms and endotherms might be a c
partial explanation of the difference in heat production fa1
between the two groups it cannot explain the differenc"
permeability
frog »m
skin «.
are »-«
both =ii
amount of "sodium-potassium pumping" (12). permeaDiiity
oi ofirug
The other question posed earlier was wh«
i n r r p fl ^ p i n m e t a b o l i c r a t e a s s o c i a t e d w i t h t h e - . . .
tfentoh^
N a + " K - - AT P a s e .
activity
ot
cells
grown
the composition of the tissues? The approximate fourfold aff
increase in metabolism of the mammal compared with co:
the reptile was associated with a 50-60% increase in th
protein content and phospholipid content of all tissuexamined (only liver and kidney were analyzed for pho
pholipid). As mentioned previously, body size influence;
metabolic
m
c
mammals is also associated with changes in the protein tween the mammalian tissues^ and the reptik.
tionship between weight-specific metabolic rate and pi
I l l U l l 111 U U t l i S l i u o b i u u s . * v * w M " " r ~ l - —
sight-specific metabolism that is about four times that is not only
;3Clll/
^iivynj^*»^.J
\—
»/•
—
—
-
---
—-
I s wbeel lt wa se et h
ne r e t b
h eei n g dmoocr eo spah ho sepxhao nl i po i idc i n at hcei dm a m( -2 2d i a c : & * * *6^)^ ^ * " £c o™
n ^t
S A
malian tissue, the fatty acid composition of these phos- from the mouse to the whale, with the more me
ENDOTHERMY AND CELL COMPOSITION
se species having a greater 22 : 6 content (14). This
lilar to the findings of the present study in that the
Dolically more intense mammalian tissues have a
sr 22 : 6 content than the less metabolically intense
ian tissues (Tables 3 and 4).
e compositional differences reported in the present
are based on a detailed comparison of only two
is. They agree with the relatively small number of
2S in the literature, but whether they represent
al differences between endotherms and ectotherms
s study of a more diverse range of vertebrate species.
thank Ann-Michelle Whitington, Patric Tap, and Namita Sen
ir technical assistance and also Dr. R. Akhmerov for his comon the manuscript. The New South Wales National Parks and
"e Service gave permission to capture the lizards.
s work was supported by a Peter Rankin Trust Fund Award (to
Use) and an Australian Research Grants Scheme grant (to A. J.
t).
lent address of P. L. Else: Dept. of Zoology, University of
lrne, Parkville, Vic 3052, Australia.
ress for reprint requests: A. J. Hulbert, Dept. of Biology, Univ.
longong, Wollongong, NSW 2500, Australia.
ed 2 May 1988; accepted in final form 3 August 1988.
:HMEROV, R. N. Qualitative difference in mitochondria of enthermic and ectothermic animals. FEBS Lett. 198: 251-255
B6.
IVTHOLOMEW, G. A., AND V. A. Tucker. Control of changes in
dy temperature, metabolism and circulation by the agamid lizard.
iphibolurus barbatus. Physiol. Zool. 36: 199-218, 1963.
NNETT, A. F. Activity metabolism of the lower vertebrates.
nu. Rev. Physiol 40: 447-469, 1978.
SE, T. J. On the evolution and adaptive significance of postnatal
>wth rates in terrestrial vertebrates. Q. Rev. Biol. 53: 243-282
78.
SSUTO, Y. Oxidative activities of liver mitochondria from mamJs, birds, reptiles and amphibia as a function of temperature.
mp. Biochem. Physiol. B Comp. Biochem. 39: 919-923, 1971.
RISTIE, W. W. Lipid Analysis (2nd ed.). Oxford, UK: Pergamon,
WSON, T. J., and A. J. Hulbert. Standard metabolism, body
aperature, and surface areas of Australian marsupials. Am. j.
ysioL 218:1233-1238, 1970.
SB, P.^L., AND A. J. HULBERT. Comparison of the "mammal
chine" and the "reptile machine": energy production. Am. J.
ysioL 240 (Regulatory Integrative Comp. Physiol. 9): R3-R9
11.
se, P. L., and A. J. Hulbert. A comparative study of the
taboiic capacity of hearts from reptiles and mammals. Comp.
•chem. PhysioL A Comp. Physiol. 76A: 553-557, 1983.
5E, P. L., and A. J. Hulbert. Mammals: an allometric study
metabolism at tissue and mitochondrial level. Am. J. Physiol.
• [Regulatory Integrative Comp. Physiol. 17): R415-R421, 1985.
5E, P. L., and A. J. Hulbert. An allometric comparison of the
ccr.ondria of mammalian and reptilian tissues: the implications
the evolution of endothermy. J. Comp. Physiol. B Biochem.
t Environ. Physiol. 156: 3-11, 1985.
;e. P. L., and A. J. Hulbert. Evolution of mammalian endormic metabolism: "leaky" membranes as a source of heat. Am.
'hysiol 253 (Regulatory Integrative Comp. Physiol. 22): R1-R7,
i.
.ch, J., M. Lees, and G. H. Sloane-Stanley. A simple
hod for the isolation and purification of total lipids from animal
ues. J. Biol. Chem. 226: 497-509, 1957.
14. Gudbjarnason, S., B. Doell, G. Oskarsdottir, and J. HallGRIMSSON. Modification of cardiac phospholipids and catechol
amine stress tolerance. In: Tocopherol, Oxygen and Biomembranes,
edited bv C. de Duve and O. Havaishi. Amsterdam: Elsevier, 1978,
p.297-310.
15. Harris, W. D., and P. Popat. Determination of phosphorus
content of lipids. J. Am. Oil Chem. Soc. 31: 124-127, 1954.
16. Hemmingsen, A. M. Energy metabolism as related to body size
and respiratory surfaces and its evolution. Rep. Steno Mem. Hosp.
Nord. Insulinlab. 9: 1-110, 1960.
17. Hendriks, T., A. A. Klompmakers, F. J. M. Daemen, and S. L.
BONTING. Biochemical aspects of the visual process. XXXII.
Movement of sodium ions through bilayers composed of retinal
and rod outer segment lipids. Biochim. Biophys. Acta 433: 271-281,
1976.
18. Hulbert, A. J. On the evolution of energy metabolism in mam
mals. In: Comparative Physiology: Primitive Mammals, edited by
K. Schmidt-Nielsen, L. Bolis, and C. R. Taylor. Cambridge, UK:
Cambridge Univ. Press, 1980, p. 129-139.
19. Hulbert, A. J., and P. L. Else. Comparison of the "mammal
machine" and the "reptile machine": energy use and thyroid activ
ity. Am. J. Physiol. 241 (Regulator,' Integrative Comp. Phvsiol. 10):
R350-R356, 1981.
20. Karasov, W. H., E. Petrossian, L. Rosenberg, and J. M.
Diamond. How do passage rate and assimilation differ between
herbivorous lizards and nonruminant mammals? J. Comp. Physiol.
B Biochem. Syst. Environ. Physiol. 156: 599-609, 1986.
21. Karasov, W. H., D. H. Solberg, and J. M. Diamond. What
transport adaptations enable mammals to absorb sugars and amino
acids faster than reptiles? Am. J. Phvsiol. 249 (Gastrointest. Liver
Physiol. 12): G271-G283, 1985.
22. Kleiber, M. The Fire of Life: An Introduction to Animal Energetics.
New York: Wiley, 1961.
23. Natochin, Yu. V., V. G. Leont'ev, M. N. Maslova, L. F.
Pomazanskaya, N. I. Pravdina, and E. M. Kreps. Sodium
reabsorption and membrane systems of vertebrate kidneys. Zh.
Evol. Biokhim. i Fiziol. 11: 45-52, 1975.
24. Lin, M. H., D. R. Romsos, T. Akera, and G. A. Leveille.
Increase in Na*,K*-ATPase enzyme units in liver and kidney from
essential fatty acid deficient rats. Experientia Basel 35: 735-736,
1979.
25. Lowry, O. H., N. J. Rosebrough, A. L. Farr, and R. J. Ran
dall. Protein measurement with the Folin phenol reagent. J. Biol.
Chem. 193: 265-275, 1951.
26. Moore, J. L., T. Richardson, and H. F. Deluca. Essential fatty
acids and ionic permeabilitv of lecithin membranes. Chem. Phys.
Lipids 3: 39-58, 1969.
27. MUNRO, H. N., and E. D. Downie. Relationship of liver compo
sition to intensity of protein metabolism in different mammals.
Nature Lond. 203: 603-604, 1964.
28. Smith. C. L. The temperature dependence of oxidative phospho
rylation and of the activity of various enzyme systems in liver
mitochondria from cold- and warm-blooded animals. Comp.
Biochem. Physiol. B Comp. Biochem. 46B: 445-461, 1973.
29. Solomonson, L. P., V. A. Liepkalns, and A. A. Spector.
Changes in (Na* + K*)-ATPase activity of Ehrlich ascites tumor
cells produced by alteration of membrane fatty acid composition.
Biochemistry 15: 892-897, 1976.
30. Wahbe, V. G., W. M. Balfour, and F. E. Samson. A comparativ.
study on vertebrate brain mitochondria. Comp. Biochem. Physiol.
3: 199-205, 1961.
31. Wharton, D. C, and D. E. Griffiths. Studies on the electron
transport system. XXXIX. Assay of cytochrome oxidase. Effects
of phospholipids and other factors. Arch. Biochem. Biophys. 96:
103-114, 1962.
32. Wilson, M. T., J. Bonaventura, and M. Brunori. Mitochon
drial cytochrome content and cytochrome oxidase activity of some
Amazonian fish. Comp. Biochem. Physiol. A Comp. Physiol. 62:
245-249,1979.
33. YORIO, T., S. TORRES, and N. Tarapoom. Alteration in mem
brane permeability by diacylglycerol and phosphatidylcholine con
taining arachidonic acid. Lipids 18: 96-99, 1983.