The chemical behaviour of dehydro-l-ascorbic acid in vitro and in vivo

Abstract

Vol. 37 PHOSPHORYLASE AND PHOSPHOROLYSIS 403 SUMMARY 1. A modified method for the preparation of phosphorylase by adsorption on A1(OH)3 is described. By this method, phosphorylase can be demonstrated in all animal tissues.2. The phosphorylase activity and the intensity of the glycogen metabolism of a tissue are shown to be positively correlated. The samte is true also of the phosphorolytic breakdown of glycogen. 3. Subcutaneous tissue possesses a highly active phosphorylase, and metabolizes glycogen ati a high rate.4. Phosphorylase is not found in the muscles of rats less than 10 days of age. In 14-day-old rats the enzyme is already comparatively active.5. Brain tissue from new-born rats shows 60 % of the phosphorylase activity of the adult brain. Phosphoglucomutase in new-born rat brain, however, was either inactive or absent. This enzyme is the limiting factor in glycogen phosphorolysis up to 14-20 days after birth, after which time its activity approaches that found in the adtlt brain.6. In intoxication by phosphorus, carbon tetrachloride' and chloroform, liver phosphoglucomutase is inactivated, but phosphorylase activity is almost normal. 7. In adrenalectomized as well as in thyroidectomized rats no decrease in glycogen phosphorolysis by muscle could be demonstrated.8. Some properties of the phosphorylase of muscle have been studied: on irradiation with ultra-violet light, or on heating to 550 for 20 min., complete destruction of the enzyme occurred. Adenylic acid diminished the inhibition caused by glucose in 2 % concentration. With 0-3 % glucose no lessening of inhibition was found when adenylic acid was added. With potato phosphorylase no inhibition of glycogen synthesis by 2 % glucose was found.9. If synthesis by muscle phosphorylase is slowed down by low temperature or by ageing of the enzyme preparation, an iodine colour reaction such as is given by glycogen can be observed after 5-10 min. of synthesis.We are indebted to Prof. Halberstaedter of the Cancer It is reasonable to assume that the function of I-ascorbic acid in the metabolism of the animal organism is that of a link in a co-ordinated chain of reactions. It might therefore be expected that, since ascorbic acid and dehydro-l-ascorbic acid constitute under certain conditions a thermodynamically reversible oxidation-reduction system, dehydroascorbic acid would become a component of these co-ordinated reactions, although under prevailing conditions it may be present in too small quantities to be detected by the available technique. With this hypothesis in view one of us started some years ago an investigation on the behaviour of dehydroascorbic acid in the guinea-pig. It was then found that whilst ascorbic acid could be almost completely recovered from the organs and tissues J. R. PENNEY AND S. S. ZILVA of the guinea-pig soon after injection, this was not the case when dehydroascorbic acid was used. It was therefore assumed that when dehydroascorbic acid (II) was present in the organism in large quantities a part of it was reduced in the body to a...

INVESTIGATIONS OF ASCORBIC ACID DEHYDROGENASE OF PEAS (PISUM SATIVUM) AND ITS DISTRIBUTION IN THE DEVELOPING PLANT

“…BUKIN (5) five minutes at pH 7.0 and 370 C, 30%o of the dehydro-ascorbic acid had hydrolyzed to 2,3-diketo-gulonic acid. PENNY and ZILVA (19,20) reported similar results. values up to 0.5 ml.…”

Investigations on The Stability and Determination of Dehydroascorbic Acid

“…The results of Penney and Zilva (1943), confirmed by the author, show. that diketogulonic acid gives about one-tenth the titre of the equivalent amount of dehydroascorbic acid.…”

“…The addition of ten parts per -million of copper (as copper sulphate), which catalyses the atmospheric oxidation of ascorbic acid, had no significant effe( t. Penney and Zilva (1943) have shown that diketogulonic acid is rendered more stable at pH 7.4 by the presence of borate, and the formation of reducing substances on treatment with hydrogen sulphide is thus eliminated. The possibility of using borate in the determination of dehydroascorbic acid was considered, as it would enable dehydroascorbic acid to be removed without giving rise to a residual titre.…”

“…of Penney and Zilva (1943)1 as destruction at pH 7.4 is extremely rapid whether in the presence or absence of borate.…”

“…It is desirable to extract at the pH of maximum stability and to obtain a blank titre after destruction of the dehydroascorbic acid under suitable conditions. Penney and Zilva (1943) found that the rate of conversion of dehydroascorbic acid to 2, 3-diketogulonic acid in citrate-phosphate buffers at 38°C. increased with pH over the range 4.0-7.4.…”