Studies on Glucuronolactonase and Gulonolactonase

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Abstract
It has been established by many authors (1–4) that D-glucurono-γ-lactone and L-gulono-γ-lactone, as well as D-glucuronic acid and L-gulonic acid, are precursors of L-ascorbic acid in animal tissues. Touster and others (5–6) found L-xylulose excreted in the urine of essential pentosuric humans and in the urine of a guinea pig fed with D-glucuronolactone. Recently, I s h i k a w a et al. (7) and Lehninger (3, 4, 8) have proved that the liver and kidneys of a guinea pig contained DPN- and TPN-specific dehydrogenases of L-gulonic acid, and that the reaction products were xylulose in the DPN system and glucuronic acid in the TPN system. Ishikawa (9) further observed that these dehydrogenases possessed activity on glucuronic acid or gulonic acid but not on glucuronolactone or gulonolactone. These reports indicated that there exists a route from d-glucuronolactone and l-gulonolactone to their corresponding acids. In the past, the presence of an enzyme activity hydrolyzing these two lactones was reported by Lehninger (3) and Eisenberg (10) in the homogenate or slices of rat liver. However, no report on the purification and detailed properties of these glucurono- and gulonolactonase has been published. In the previous report (11) on the distribution of lactonase in various animals, Y a m a d a et al. showed that gulonolactonase seemed to play a significant role in the biosynthesis of l-ascorbic acid. The present paper describes the preparation and purification of the enzyme, together with an account of some of its properties. In this study, the distribution of lactonase activity in cell fractions showed the presence of two evidently different lactonases, tentatively named Lactonase-I and -II for soluble and microsomal fractions, respectively.

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