In the citric acid cycle, the reaction which produces succinyl CoA also forms carbon dioxide. The key intermediate enzymic step involves:: (A) The decarboxylation of a hydroxy acid, (B) The decarboxylation of an alpha-ketoacid, (C) The decarboxylation of a beta-ketoacid, (D) The oxidation of a keto group to a carboxylic acid
Answer is B. The enzyme is a-ketoglutarate dehydrogenase, an a-keto acid, which is decarboxylated. Therefore the second choice is correct. The only confusion might be with the last choice, since in effect it involves the oxidation of a keto group to a carboxylic acid. However, the product is the thio-ester of a carboxylic acid.