1991 Volume 39 Issue 7 Pages 1792-1795
The metabolism of L-tryptophan by Saccharomyces uvarum (carlsbergensis) was investigated by simultaneous measuring of fluxes through kynureinase, through transaminases and into protein using L-[methylene 14C]-and L-[side chain-2, 3-3H]tryptophan. In yeast cultivated in synthetic medium (S medium), the flux into protein was predominant, closely followed by the flux leading to 2-3H liberation. The proportion of L-tryptophan metabolized via the latter fluxincreased over 10-fold (75% of total tryptophan metabolized) as the concentration of L-tryptophan was raised from 5×10-5 to 5×10-4M. L-Tryptophan metabolized via the kynureninase flux was less than 5% of total tryptophan metabolized. In yeast extract-polypepton-glucose medium (YPG medium), more tryptophan was incoporated into protein than in the S medium. Contribution of the kynureninase flux remained very low. Tryptophan metabolism via each flux changed depending on the growth phase. 2-3H liberation was shown to be primarily due to tryptophol synthesis by high performance liquid chromatography (HPLC) and nuclear magnetic resonance (NMR), indole-3-acetic acid and kynurenic acid also contributing to 2-3H liberation but to a much lesser extent. 2-3H liberation increased dose-dependently at tryptophan concentration higher than 10-5M, while the kynureninase flux reached its plateau at 10-5M. Formation of tryptophol and indole-3-acetic acid via indole-3-pyruvic acid and indole-3-acetaldehyde with indole aldehyde as a by-product was confirmed using exogenous tryptophan metabolites with indole rings.
