Subcellular Localization of Isoleucine-Valine Biosynthetic Enzymes in Yeast

By using the method of stepwise homogenization of yeast spheroplast lysates employed previously with the leucine biosynthetic enzymes, it is shown that threonine deaminase, acetohydroxy acid synthase, Mg(2+)-dependent isomero-reductase, and dihydroxy acid dehydratase are particulate. Density gradient centrifugation and the behavior of marker enzymes suggest that all of the above enzymes of the isoleucine-valine biosynthetic pathway are associated with the mitochondria.