Life, death and membrane bilayers
2003
SUMMARY Membrane bilayers are essential elements of life, and the synthesis of the
hydrocarbons that make up membrane bilayers may have preceded the appearance
of life on Earth. Membrane-associated processes are significant components of
metabolism, and the acyl composition of membrane bilayers is associated with
metabolic activity in a predictable manner. This has resulted in the `membrane
pacemaker9 theory of metabolism, which proposes that the relative balance
between monounsaturated and long-chain polyunsaturated acyl chains in membrane
bilayers is a fundamental determinant of metabolic rate of a species. The
omega-3 polyunsaturated docosahexaenoate is an especially important component
of membranes in this regard. Whilst it is suggested that the physical
properties of membrane polyunsaturates are important with respect to their
influence on metabolic rate, it is their chemistry that is important in aging.
Membrane acyl composition is related to maximum lifespan in mammals and birds,
probably via their role in lipid peroxidation. Calorie restriction
modifies acyl composition of membrane bilayers and is associated with
decreased membrane lipid peroxidation and lifespan extension. The membrane
pacemaker theory of metabolism has given birth to the membrane pacemaker
hypothesis of aging, which will require further investigation.
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