TERMINAL OXIDATION SYSTEM IN RESPIRING YEAST

Abstract

A yeast lactic dehydrogenase containing cytochrome b2 and a certain flavin(s), but completely free of cytochrome c was used as an enzyme solution. The anaerobic oxidation of lactate by this enzyme solution, determined by the reduc -tion of cytochrome b2, was 2-3 times faster than that of malate. The optimum pH was 4-5.5 for lactate and 8-9 for malate. In this enzyme solution cytochrome b2 was shown to be highly autoxidizable. 10-4 10-6 [image] flavin mononucleotide and flavin adenine dinucleotide evidently inhibited the dehydrogenase activity. The reduction of cytochrome c by this enzyme dehydrogenase by the presence of lactate occurred at a much higher rate than did the reduction of cytochrome b2. It is assumed that cytochrome b2 in the enzyme preparation may be in quite different state from the intact state in yeast cell, where cytochrome b2 presumably forms an efficient conjugate with the dehydrogenase-flavin moiety.