Download The Evolution of Endothermy: Role for Membranes and Molecular

The Evolution of
Endothermy:
Role for Membranes
and Molecular Activity
By
Paul L. Else, N. Turner and A.J. Hulbert
Endothermy in Vertebrates:
A Defining Property
Characteristics
 High Rate of Metabolism/Oxygen
(Compared to
Ectotherms)
Consumption
 Tissues have high levels of aerobic
enzyme activity
 Large mitochondrial volume and
membrane densities (Table 1)
 Internal organs are larger
 Organisms with a “high cost of living”
which impact every aspect of their life.
Why is there a higher
rate of metabolism/O2
consumption???
There are differences in the overall rates of
cellular processes when comparing endotherms
to ectotherms.
(ex. Sodium pump / Protein synthesis
Three Models of Metabolism Show
Recurring Themes
 Compared body temp between
ectotherms and endotherms
(vertebrates) and mass-matched
species.
 Compared animals of varying body mass
within a vertebrate class
 Metabolic changes that occur during
different phases of mammalian
development
The Three Ideas of Membrane
Pacemaker Theory of Metabolism
 Only a few cellular processed consume
most of the energy used by most
organisms

Ex. Na+/K+ pump drives other processed
(moves other ions across membranes)
 What does this say????

No new or special processes acct for the
differences in metabolism between species
Pacemaker Theory (continued)
 Energy consuming processes acct for
similar proportions/% of metabolism in
animals with very different rates of
metabolism


What does this say???
The amt of energy associated with a
process may be different among species,
but as a percentage of metabolic rate, it is
similar.
Pacemaker Theory (cont.)
 Most processes are directly or indirectly
linked to membranes.

(examples – maintenance of ion gradients,
protein synthesis, etc.
 What does this mean…

The variations in animal metabolism is due
to MEMBRANES setting the pace of a
small number of Energy consuming
processes.
And thus the Membrane
Pacemaker Theory of
Metabolism…
was born!!!!!
Testing the Theory
 “The Sodium Pump”
A ubiquitous protein in the cells and
tissues of all animals
 Endotherms vs. Ectotherms tissues
 There are no differences in the number
or density of sodium pumps
 There are differences in the rate of
enzyme activity/ molecular activity.
 (Figure 1)
Sodium Pump Study
More Findings…
 Changes in the Pump molecular activity
is common during development
Study of the Membrane Environment
 Ectotherms have more monounsaturated
membranes and fatty acids with only one
C=C.
 Endotherms compared to Ectotherms,
Smaller compared with Larger –sized
mammals and birds, and adult compared
with young mammals tend to have
higher molecular activities and fatty
acids with more C=C double bonds.
Membrane “Crossover”
Experiments
 Used tissues from rat (with high mol.
Activity)

Brain and Kidney
 Used same tissues from toad (low
molecular activity.
 METHOD- detergent to lower activity to
similar levels between the two, heat to
destroy pump while fatty acid comp
remained same.
Cross Over
 Enzyme activity was reconstituted with
same species membrane

Mol activ. Back to normal level
 Membrane reconstituted with membrane of
another species.


Mol activ. Shifts to the added membranes
orig.activity.
Ex. Toad added to rat…reduced Mol. Act.
 Other CO exper- During Development

Similar Findings
Possible Mechanisms
 The use for polyunsaturates suggests an
improvement in the activity of membrane
proteins.
 Looked at differences in acyl
composition of membrane which
suggests an altering of the electrical
fields within the bilayer

It is still unknown how they influence lipid
protein interactions.
Mechanisms (continued)
 Experiments on Physical Properties of
Membrane Lipids and influence on
Molecular activity

Shows increasing molecular activity with
increasing area occupied by lipids.
 What does this say???


MA and area lipids correlate to
polyunsaturation and
Electrical field strengths are dispersed by
the “kinked” carbon chains of the
unsaturated lipids
Summing it up
 During evolution, as body mass
increased, there was a need for animals
to reduce their mass-specific met rates.

(too little surface area to get rid of their
heat)
 Membrane lipid composition becomes
important.
 If, during evolution, increased
polyunsaturated membranes occurred,
then an increase in Molecular activity
would occur