Oxidation of phosphohexonate and pentose phosphoric acids by yeast enzymes

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Abstract
I. An enzyme was prepared from Lebedew maceration fluid by precipitation at pH 4.6, washing with acid and drying, to study the oxidation of phosphohexonic acid. The optimum activity was between pH 6.3-7.5. The action was inhibited by phosphate like the hexose monophosphate system, but less powerfully. With pure coenzyme II oxidation of phosphohexonic acid proceeded until 1/2 O2 per mol. was consumed. At this stage the product, prepared as a Ba salt, consisted of a mixture of phosphoketohexonate and phosphopentonic acid, as judged by its analysis and mode of prep. When less pure coenzyme was used the reaction proceeded further, the end-products and end-point being altered. The O2 uptake and CO2 output were each about 1 m. per m. substrate; an amt. different from that seen in expts. of Warburg Christian [1937] with a different prep. of enzyme. Among the end-products an analytically pure compound corresponding to a phosphorylated 4-C monocarboxylic dihydroxy acid[long dash]possibly phosphoerythronic acid[long dash]was isolated. Two other fractions gave definite reactions for pentose by Bial''s test. II. Lebedew maceration fluid from dried brewers'' yeast oxidized d-ribose-5-phosphoric acid vigorously, and to a less extent d-arabinose- and xylose-5-phosphoric acids. When phenazine methochloride was the carrier the latter 2 substrates were not appreciably oxidized. The activity was destroyed by boiling. The acetate precipitate from Lebedew fluid was feeble towards pentose phosphates, at least with phenazine methochloride as carrier. An active dialysed prep. was made from Lebedew fluid; it could be kept as dry powder and was inactive without the addition of coenzyme II. With coenzyme oxidation was vigorous with ribose phosphate, only about 1/2 as fast with the other pentose phosphates. CO2 evolution and O2 absorption were about equal to 1 m. of each per m. pentose phosphate. Laked horse blood oxidized ribose phosphate slightly in presence of methylene blue; the other 2 pentose esters were not attacked. Intact cells being impermeable to phosphoric sugar esters did not oxidize them, nor were the pentoses oxidised by brain slices. Kidney slices readily oxidized 2-keto-d-gluconic acid.

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