Mechanisms of carbonyl participation in phosphate ester hydrolysis and their relationship to mechanisms for the carboxylation of biotin

Abstract

The enzymic reaction of biotin with bicarbonate and ATP produces N-carboxybiotin, ADP, and phosphate. The intermediates in the reaction are unknown. It has been proposed that the intramolecular reaction of the carbonyl hydrate of methylacetoin diethyl phosphate (1) may serve as a model for the latter part of such a mechanism. In basic solution, 1 reacts rapidly to give two sets of products that can be accounted for by a mechanism involving addition of a hydroxyl group of the carbonyl hydrate to the adjacent phosphate. The rapid reaction of the nonenolizable ester with base rules out earlier mechanistic proposals of the reaction involving an enolization pathway