The lysine requiring mutants of Neurospora crass, whenclassified by the criteria of symbiotic, specificityof growth requirements, intersterility and genetic recombination,fall into five groups representing at least five loci.Members of two groups are capable of growth on a minimalmedium supplemented with either lysine, ∈-hydroxynorleucineor α-aminoadipic acid. Members of a third group can utilizelysine or ∈-hydroxynorleucine, while members of the fourthand fifth group are unable to grow in the absence of lysine itself.
The D-isomers of all these amino acids stimulate growth in the presence of the natural isomers.Nevertheless theirα-keto analogues when added to the medium are without effect. Since it has been shown that Neurospora has enzymes catalyzing the interconversions of α-aminoadipic and α-keto-adipic acids, the nonutilization of the exogenous keto acidsis ascribed to a failure of assimilatory mechanisms.
Investigations of the incorporation of isotopic nitrogen into the mycelial lysine indicate that both the α and ∈-amino groups are quite stable. Inasmuch as the nitrogen of α-aminoadipic acid is labile it is suggested that the degradation of lysine via that acid is not quantitatively significant.
None of a number of other substances which might be postulated either as precursors of α-aminoadipic acid oras intermediates between that acid and lysine has any effect on growth. Syntheses of several of these compounds are described.
