The metabolism of protocatechuic acid by a vibrio

Abstract

Protocatechuic acid is oxidized by crude extracts of Vibrio O1 to [beta]-oxoadipic acid; partially purified extracts yield stoicheiometric amounts of [beta]-carboxymuconic acid. Heat-treated extracts of the vibrio accumulate a lactone from either protocatechuic acid or [beta]-carboxymuconic acid. The lactone has been isolated and identified as (+) -4-hydroxyhex-2-enedioic 1[long dash]4-lactone [(+)-muconolactone]. Enzymic synthesis of (+)-muconolactone from /3-carboxymuconic acid is accompanied by loss of carbon dioxide. Neither cis-cis-muconic acid nor [beta]-carboxymuconolactone is attacked by vibrio extracts grown with p-hydrox-ybenzoic acid as carbon source, so the lactonization and decarbox-ylation appear to occur simultaneously. Some properties of the lactoni-zing and delactonizing enzymes are described and compared with similar enzymes from other micro-organisms. In particular, a metal requirement and sulphyrdryl groups are associated with the lactonizing enzyme of Vibrio, the amount of which in cells is markedly increased by growth on p-hydroxybenzoic acid. The significance of symmetric and asymmetric lactones is discussed in relation to new and distinct modes of aromatic ring fission.