Multiple Molecular Forms of Pyruvate Kinase from Mucor rouxii

Pyruvate kinase from Mucor rouxii constitutes a family of three isoenzymes which can be separated in DEAE‐cellulose columns. These have been named type I, II and III. They also have different electrophoretic mobility in polyacrylamide gels. Pyruvate kinases type I, II and III were partially purified by ion‐exchange chromatography. Antisera were prepared against types I and III. The antigenic behaviour of the three isoenzymes supported the hypothesis on the hybrid nature of pyruvate kinase type II and confirmed the identity of pyruvate kinase from yeast‐like cells and type I from mycelium. The filamentous form contains the three types, none of them being constitutive and the proportion of each depends on the concentration and on the nature of the carbohydrate in the growth medium. Under gluconeogenic conditions of growth type III predominantes while in any condition in which aerobic glycosis is favoured type I is the dominant form. Aerobic or anaerobic yeast‐like cells which display a fermentative mode of hexose utilization contain exclusively the type I isoenzyme. Addition of glucose or xylose to a 17‐h‐old cultures devoid of carbohydrates leads to the reappearance of pyruvate kinase I and II activities. Experiments with cycloheximide and actinomycin D indicate that this process requires protein synthesis. Results of preincubation of mixtures of extracts under several conditions indicate that the system of three pyruvate kinases does not represent proteolytic degradation of a single enzyme or interconvertible forms of the same enzyme.