Studies on Phosphomannose Isomerase

Abstract

Abstract Phosphomannose isomerase isolated from brewers' yeast was found to be inhibited in a time-dependent process by 8-hydroxyquinoline, ethylenediaminetetraacetate, o-phenanthroline, α,α-dipyridyl, cysteine, and dithiothreitol. The effectiveness of these agents in bringing about inhibition paralleled their ability to bind zinc, and the inhibition could be prevented by blocking the coordination sites of the metal-binding agents. An instantaneous reversal of inhibition occurred upon the addition of metals to the EDTA-inhibited enzyme, and the extent of reversal or prevention of inhibition was proportional to the ability of the added metals to form a complex with EDTA. Metal analyses, performed by atomic absorption spectrophotometry, yielded a metal content of 1 g atom of zinc per mole of enzyme (molecular weight, 45,000). Other metals were found to be either absent or present only in stoichiometrically insignificant concentrations. From inhibition data and metal analyses before and after inhibition, it is concluded that EDTA forms the inactive apoenzyme by removal of zinc from the active metalloenzyme.