STUDIES ON THE ISOLEUCINE PRECURSOR α,β-DIHYDROXY-β-ETHYLBUTYRIC ACID

A mutant strain of Neurospora crassa (no. 16117) was shown by Bonner, Tatum, and Beadle (1943) to require the amino acids isoleucine and valine for growth. Later Bonner (1946) presented evidence that the double requirement was due to the accumulation of an isoleucine precursor, which then inhibited conversion of some analogous intermediate in valine synthesis. At that time it was suggested that the respective keto acids were involved. Further experiments by Adelberg, Bonner, and Tatum (1950) revealed that although filtrates of strain 16117 contained no detectable "keto-isoleucine," they had high potency for the isoleucine-requiring Escherichia coli strain 58-336. The factor responsible was isolated and characterized as a ,,8-dihydroxy-,B-ethylbutyric acid, i.e., the dihydroxy precursor of isoleucine. The present paper, which deals with further aspects of this problem, consists of three parts: the assay and production of "dihydroxy-isoleucine," which will be referred to simply as "precursor"; quantitative data on its biological activity; and the nutritional evidence for assigning it the role of a normal biosynthetic intermediate.

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