METABOLISM OF d-GLUCURONOLACTONE IN MAMMALIAN SYSTEMS. 3. FURTHER STUDIES OF d-GLUCURONOLACTONE DEHYDROGENASE OF RAT LIVER

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Abstract
Rat-liver D-glucuronolactone dehydrogenase had a pH optimum at about pH 6[center dot]5 and maximum stability over the range pH 5[center dot]5-7[center dot]0. The enzyme was specific for nicotinamide adenine dinucleotide (NAD) and did not oxidize D-galacturonic acid or D-mannuronolactone. The affinity of the enzyme for NAD was considerably greater than that for D-glucuronolactone. No reversal of the reaction could be demonstrated with D-glucaric acid or its lactones and NADH2 as substrates. Non-competitive inhibition of the enzyme, obtained from rat or guinea-pig liver, was exhibited in the presence of barbiturates and of aliphatic alcohols. The magnitude of this effect increased with the water-insolubility of the inhibitors.