REGULATION OF OXIDATIVE PHOSPHORYLATION

Depends upon substrate availability and energy demands in the cell.
Important substrates are NADH, O2, and ADP.
As ATP is used, more ADP is available, translocated through adenine nucleotide translocase
--> electron transport increases.
Known as respiratory control.
Helps to replenish ATP pool in the cell, which is kept nearly constant.
Rates of glycolysis, citric acid cycle, and electron transport system are matched to a cell’s
ATP requirements.
Proton gradient can be short-circuited to generate heat
Found in brown adipose tissue in newborn mammals and animals that hibernate, and animals
adapted to cold conditions
A protein called thermogenin forms a proton channel in inner mitochondrial membrane -->
dissipates proton gradient, but electrons still flow --> heat production
Pathway is activated by fatty acids from triacylglycerol catabolism from epinephrine
stimulation
Superoxide Production
Even though cytochrome oxidase and other proteins that reduce oxygen have been designed not to
release O2
.- (superoxide anion), it still does happen.
Protonation of superoxide anion yields hydroperoxyl radical (HO2
.), which can react with another
molecule to produce H2O2.
Enzyme superoxide dismutase catalyzes this reaction
2H
+
O2
.- + O2
.- ----------------------------> H2O2 + O2
superoxide dismutase
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Recent findings have indicated that superoxide dismutase mutations can cause amyotrophic lateral
sclerosis (Lou Gehrig’s disease), in which motor neurons in brain and spinal cord degenerate.
The hydrogen peroxide formed is scavenged by catalase:
H2O2 + H2O2 2H2O + O2
catalase
Peroxidases catalyze an analogous reaction:
ROOH + AH2 ROH + H2O + A
peroxidase