Enzymatic Studies of D-Arabinosone

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Abstract
A NADPH2-linked enzyme, tentatively called “aldehyde reductase” was purified about 130 fold from baker's yeast. This enzyme acted on several osones, DL-glyceraldehyde, D-glyceraldehyde, D-erythrose, D-threose, D-glucuronolactone and benzaldehyde; hexoses, pentoses, maltose and acetaldehyde were inactive and NADH2 did not replace NADPH2. Km values for NADPH2 DL-glyceraldehyde, D-arabinosone and D-glucosone were 5.9×10−3M, 3.4×10−4M, 4.0×10−3M and 1.4×10−3M, respectively. The enzyme was activated with SO4−− ion and was not affected by EDTA as in the case of aldose reductase (2). Existence of an isozyme of aldehyde reductase was suggested from the results of DEAE-cellulose column chromatography. Another NADPH2-linked osone-reducing enzyme was also purified about 50 fold from baker's yeast. This enzyme was able to reduce D-arabinosone, L-arabinosone, D-xylosone, D-glucosone and very slowly L-ascorbic acid; other sugars tested, and benzaldehyde and acetaldehyde were inactive and NADH2 could not substitute for NADPH2. The name “osone reductase” was suggested for the enzyme. Km values were calculated to be 2.0×10−2M for D-arabinosone, 2.4×10−2M for D-glucosone and 1.1×10−5M for NADPH2. The enzyme was completely inhibited by 2×10−5Mp-chloromercuribenzoate. EDTA showed significant inhibition on the activity. Ag+, Zn++, Fe++ and Fe+++ ions were also strongly inhibitory. We devised an assay method by which osone reductase could be assayed separately when aldehyde reductase existed together.

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