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

Abstract

Conditions for the production of the isoleucine precursor, alpha,beta-dihydroxy-beta-ethylbutyrate, by a mutant of Neurospora crassa are described. Biological assay methods included a relatively precise turbidimetric assay and a fast auxanographic method. For assay purposes a mutant of Escherichia coli requiring isoleucine was used, or else wild-type E. coli (strain K-12) inhibited by valine. The response of the E. coli mutant to the precursor was studied quantitatively, and it was found that the compound was used non-adaptively at maximal rate, following a lag-period which was inversely proportional to substrate concentration. A collection of Neurospora and bacterial isoleucine mutants were classified on the basis of their response to this and other isoleucine precursors, and a tentative scheme for isoleucine biosynthesis presented.