Isoleucine and Valine Metabolism in Escherichia coZi

On the basis of isotopic results obtained with Torulopsis utilis and Neurospora crassa, Strassman et al. (1) and Adelberg (2) have proposed a mechanism for valine biosynthesis in which pyruvate is converted to a-acetolactate. Acetolactate would then undergo a rearrangement to yield the carbon skeleton of valine. Abelson (3) showed that pyruvate, in competition with glucose, gave rise to the carbons of valine in Escherichia coli. This paper will show that extracts of E. coli do indeed have an acetolactate-forming enzyme, and evidence will be presented that this enzyme plays an essential role in valine biosynthesis. Preliminary reports of part of this work have been presented elsewhere (4, 5).