Respiratory Chain-linked Lactic Oxidase of Bakers' Yeast

Abstract

VARIOUS forms of lactic dehydrogenase (not iso-enzymes) are reported in yeast¹. Apart from one specific for D(−) lactate in the soluble constituents of the yeast cell, Morton observed that there exists in the particulate fraction of anaerobic yeast a lactic dehydrogenase which is a flavoprotein (free from hæem) specific for D(−) lactate whereas the enzyme in the particles of aerobic yeast, the hæmo-flavoprotein, is specific for L(+) lactate². The D (−) lactic dehydrogenase has been purified and studied by Nygaard³ and Gregolin and Singer⁴. The physiological significance, however, of lactic dehydrogenase or lactic cytochrome c reductase has not been found. Gregolin and Singer⁴ could not find oxygen consumption in particles of aerobic yeast with D(−) lactate as substrate unless external cytochrome c had been added, and hence concluded that the enzyme is not directly linked to the cytochrome system of yeast, at least in the respiratory particle preparation. This note, however, reports a lactic oxidase in a preparation of mitochondrial particles from aerobic bakers' yeast (Saccharomyces cerevisiae) oxidizing D(−) lactate.