THE BIOSYNTHESIS OF ISOLEUCINE AND VALINE IN NEUROSPORA CRASSA

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Abstract
Experimental data show that [alpha]-aceto-[alpha]-hydroxy butyric acid and a-acetolactic acid are converted to [alpha],[beta]-dihydroxy-[beta]-methylvaleric acid (I) and [alpha],[beta]-dihydroxyisovaleric acid (n) by cell free extracts of N. crassa, strain 16117. Compounds I and II, previously postulated to be intermediates in the biosynthesis of isoleucine and valine, are converted to these amino acids by cell-free extracts of N. crassa, wild type. An enzyme that actively converts [alpha]-keto-[beta]-hydroxy-[beta]-methyl valeric acid and [alpha]-keto-[beta]-hydroxy-isovaleric acid to the corresponding dihydroxy compounds is present in these extracts. This enzyme specifically requires reduced TPN for activity and is without activity on closely related substances such as [alpha]-ketoisovaleric acid. All available evidence indicates that these a-keto-[beta]-hydroxy acids are intermediates in the conversion of [beta]-keto-[alpha]-hydroxyacids to the dihydroxy acid precursors of isoleucine and valine.