A yeast with unusual sulphur amino acid metabolism

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Abstract
SUMMARY: Activities of the polyol dehydrogenases of Puccinia graminis f. sp. tritici were surveyed by measuring polyol-dependent rates of reduction of NAD+ and NADP+ in cell-free extracts of axenically-grown mycelia. Seven of the eight polyols tested caused NADP+ reduction, with highest activity for d-glucitol, followed by l-arabitol, xylitol, erythritol, galactitol and ribitol, and low activity with d-arabitol; only d-mannitol failed to support activity. Inactivation rates were consistent with at least three separate enzymes, specific for d-glucitol, xylitol and l-arabitol respectively, with apparent Km values of 170--198 mM for xylitol and d-glucitol (Km for NADP+ 36--55 μM), and 34 mM for l-arabitol (Km for NADP+ 1·2 μM). The NADP+-dependent activities were almost completely inhibited by 2 mM-dithiothreitol, in contrast to the NAD+-dependent activities, which were stimulated. NAD+-dependent activity was highest with d-mannitol, followed by successively lower activities with d-arabitol, xylitol and d-glucitol, with no activity with any of the other polyols; each of the four active polyols appeared to be oxidized by a different enzyme. All four NAD+-dependent activities were rapidly lost after Sephadex treatment of crude extracts.