Studies in valine biosynthesis: II. Enzymatic dehydration of α,β-dihydroxyisovaleric acid by plant extracts

The dehydration of a, /3-dihydroxyisovaleric acid to a-ketoisovaleric acid is an intermediate step in the biosynthesis of the amino acid, valine. The dehydrase that catalyzes this conversion was first observed in the mold, Neurospora crassa and in a bacterium, Escherichia coli (12). More detailed studies on the dehydrase of baker's yeast, Saccharomyces cerevisiae have been reported (22). Recently the dehydration of a, /3-dihydroxyisovaleric acid was found to be catalyzed by cell-free extracts of Torulopsis utilis, Serratia marcesens, Bacterium cadaveris, and Micrococcus lysodeikticus (23). All of the above seven organisms are able to grow with an inorganic nitrogen source and thus can synthesize all of their amino acids. The above two characteristics are likewise shared by higher plants. Verification is found in the nutritional requirements of plant organs in aseptic tissue culture. However there have been no reported studies to date on the pathway of valine biosynthesis in higher plants. In this connection and to continue the above dehydrase distribution studies, this enzymatic activity was found in crude extracts of Chlorella pyrenoidosa. As the photosynthetic algae and fungi, including the above bacteria, belong to the