The lactic dehydrogenases of yeast: II. The identification of the l(+) lactic dehydrogenase of “petite” yeast as cytochrome b2

The respiratory deficient “petite” mutants of yeast are noted for the absence of most of the cytochromes present in normal cells, including cytochromes of the b type. Thus the oxidation of l(+) lactate by such cells could not be readily ascribed to the operation of the hemoflavoprotein cytochrome b 2. In order to decide whether the enzyme responsible is cytochrome b 2 or another dehydrogenase not present in the wild strain, the enzyme was isolated from “petite” cells. On the basis of the comparison of their absorption spectra, catalytic properties, and other characteristics, the l(+) lactic dehydrogenases isolated from normal and “petite” cells have been shown to be identical. The reason why its presence had escaped detection by spectroscopic methods is that its concentration in the mutants is below the limit of the sensitivity of the techniques previously employed.