The relation between biotin and tryptophan metabolism studied in Neurospora crassa

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Abstract
[gamma] -(3:4-Ureylenecyclohexyl)butyric acid, an antimetabolite of biotin, inhibits the utilization of tryptophan by a nicotinic acid-requiring mutant of N. crassa (39401) and this inhibition is overcome by the addition of biotin. This indicates that biotin is involved in the metabolism of tryptophan. Biotin functions only in the tryptophan-formylkynurenine reaction and the utilization of formylkynurenine is not affected by biotin de-ficiency. The ureylene derivative does not affect the utilization of other intermediates in the conversion of tryptophan into nico-tinic acid such as formylkynurenine, kynurenine, 3-hydroxy-kynurenine, 3-hydroxyanthranilic acid and nicotinic acid. In vitro studies with suspensions of Neurospora mycelia show an accumulation of tryptophan during biotin deficiency, and it is suggested that biotin may be involved in the formation of an un-known intermediate between tryptophan and formylkynurenine.