Conversion of L-Gulonolactone to L-Ascorbic Acid; Properties of the Microsomal Enzyme in Rat Liver

Regulation of Ascorbic Acid and of Xylulose Synthesis in Rat-Liver Extracts. The Effect of Starvation on the Enzymes of the Glucuronic Acid Pathway

“…Chatterjee, Ghosh, Ghosh & Guha (1958), Chatterjee et al (1960a,b), Kar, Chatterjee, Ghosh & Guha (1962) and Suzuki et al (1960) gave evidence for the direct conversion of glucuronolactone into gulonolactone and then into ascorbic acid by preparations of purified microsomes, provided that cyanide or pyrophosphate was added at relatively high concentrations. The present experiments with potassium chloride and sucrose extracts containing the supernatant as well as the microsomes and in which ascorbic acid is formed without the requirement for cyanide give probably a more physiological representation of what may occur in the whole living cell.…”

“…According to Chatterjee et al (1960a), Suzuki, Mano & Shimazono (1960) and Yamada et al (1962) glucuronolactone could be converted into gulonolactone either by direct reduction or via gulonic acid after hydrolysis to glucuronic acid. The latter seems to be the prevalent pathway operating in the liver extracts used in present experiments.…”

Further observations on the intracellular location and mechanism of action of liver enzymes catalysing the synthesis of l-ascorbic acid

“…ConverBion of ethyl D-glucuronate and methyl Dglucuronate into L-a8corbic acid. Suzuki et al (1960) reported that incubation of ethyl D-glucuronate with rat-liver microsomes in the presence of 0-05M-potassium cyanide led to the formation of L-ascorbic acid. We have also observed this with Table 3.…”

Enzymatic Studies on the Metabolism of Uronic and Aldonic Acids Related to L‐ascorbic Acid in Animal Tissues*

“…The enzyme appears to be specific for the lev0 C-2 hydroxyl group of pentonic and hexonic acid lactones. 19 The free acids corresponding to the tested lactones and L-rhamnolactone were completely inactive. The lactone structure and the terminal alcohol group seem to be essential for the activity.…”

“…The activity of this enzyme was observed in microsomes prepared from rat liver." The assay conditions were as follows: 19 The incubation was carried out in Warburg flasks containing 10 pmoles of substrate, microsomes from 0.4 gm. of rat liver, and 1.50 pmoles of phosphate buffer, PH 7.0, in a final volume of 3.0 ml., in an atmosphere of oxygen, for 30 min.…”