Hemoprotein formation in yeast. VI. Mutants with changed levels of catalase and of other heme enzymes under conditions of glucose repression.

Three mutants with altered response of the hemoprotein level to glucose repression and anoxia were characterized biochemically. Two mutants show complete resistance of catalase activity to glucose repression and a lower degree of resistance of cytochrome c oxidase and of some other enzymes. Liquid nitrogen spectra of these mutants grown in high glucose medium are typical for those of glusoce-derepressed spectra of wild-type cells. The third mutant is hypersensitive to glucose repression and shows only traces of catalase T activity when grown in high-glucose media. In these conditions its spectrum is almost devoid of typical peaks of cytochromes. When grown on ethanol or raffinose it forms catalase and shows a typical derepressed spectrum of cytochromes. The regulatory mechanism impaired in the mutants is not known. It seems likely that the regulation of the heme pathway in the mutants does not differ from that of the wild-type.