Question

A) Addition of malate to an extract of muscle cells stimulates oxygen consumption by the extract. Explain why malate stimulates oxygen consumption.

B) Malonate is an inhibitor of succinate dehydrogenase. If malonate is added to a suspension of bacteria that are catabolizing glucose then oxygen consumption is inhibited. Explain why malonate inhibits oxygen consumption.
C) Which intermediate do you expect to accumulate in the presence of malonate?
D) Besides simply removing malonate, can you suggest a treatment that would reverse the inhibition caused by malonate?

Answer 1

A. Malate is the anionic form of malic acid, a dicarboxylic acid, and is an intermediate in the citric acid cycle (TCA cycle).

when the malate extract is added it can repair the intermediates products of other biosynthetic reactions, when they have been completely recovered, small amounts of malate can generate oxidation catalysts of large numbers of AcetylCoA, which increases the oxygen requirement

B. Malonate is an inhibitor of the enzyme succinate dehydrogenase which is in competition with succinate and binds to the active site of the enzyme without generating any reaction. one of the enzymes of the TCA complex is succinate dehydrogenase, which is also part of complex II of the electron transport chain, if it is inhibited a chain reaction is generated by stopping the TCA cycle, oxidative phosphorylation and feedback reduces the oxidation of pyruvate to Acetyl CoA, finally leading to lower oxygen consumption

C. Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. If the malonate inhibits this enzyme, accumulation of succinate occurs.

D. Malonate is a competitive inhibitor, which does not require mechanisms to bind to the active site of the enzyme, its action can be reversed by increasing its competitive substrate, succinate.