Uridine Diphosphoglucose Dehydrogenase Research Articles

Uridine diphosphoglucose dehydrogenase from rat liver: Purification and effect of pH on regulatory properties

Uridine diphosphoglucose (UDPG) dehydrogenase (UDPglucose:NAD + oxidoreductase, EC 1.1.1.22) has been purified to apparent homogeneity from rat liver supernatant (105 000 × g). The enzyme was found to be NAD + specific and had maximal velocity at pH 9.4. It was also fairly active at pH 8.6 and under these conditions, it was allosterically inhibited by UDPxylose. However, at pH 9.4 the inhibition by this compound was competitive in nature. In the absence of the coenzyme, the enzyme could bind the substrate rather firmly. The binding of the substrate at pH 9.4 was accompanied by alterations in the protein resulting in partial dissociation of subunits as could be seen from the elution profiles on Sephadex G-100. The addition of the coenzyme prevented these changes. The enzyme showed an approximate molecular weight of 300 000 and seemed to be tetrameric after sodium dodecyl sulphate treatment. The kinetics of the enzyme in the native form and the dissociated state showed variations in affinity for the substrate with the respective K m values of 7.56·10 −5 M and 1·10 −3 M. This was in keeping with the amount of substrate ([U- 14C]UDPG) retained on the kinetically inactive enzyme in undissociated and dissociated forms. The results show that the pH-dependent loss of regulatory property was related to the substrate-induced partial disaggregation of the protein.

Effect of adrenalectomy and hypophysectomy on responses of rat liver enzymes to high-fructose diets.

The effect of dietary fructose on the activities of a number of enzymes was studied in normal, adrenalectomized, and hypophysectomized male Sprague–Dawley rats. The effect of feeding a high-fructose diet on relative liver size, soluble protein, glycogen, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, phosphoglucomutase, glyceraldehyde-3-phosphate dehydrogenase, and glucose-6-phosphatase was not appreciably altered by endocrinectomy. It appears, therefore, that the fructose effect on these rat liver constituents is not mediated by adrenal or pituitary hormones, although endocrine function may influence enzyme activity. The enzymes which were not particularly affected by either endocrinectomy are those associated with the metabolism of phosphorylated intermediates.The fructose diet increased the activities of L-α-glycerophosphate dehydrogenase and lactic dehydrogenase to a greater extent after endocrinectomy; therefore, an inhibition of the fructose effect in normal animals by endocrine function was postulated. The effect of feeding fructose on the activities of the pentose-phosphate-metabolizing enzymes and glutaminase was abolished by hypophysectomy. In this case it was postulated that pituitary function is required for the fructose effect as a permissive agent. The fructose-mediated increases of malic enzyme and uridine-diphosphoglucose dehydrogenase were diminished in magnitude after endocrine removal, but not abolished.The activities of the urea-cycle enzymes, transaminases, and serine dehydrase were not increased by fructose feeding. The relationship between the fructose effect and endocrinectomy appeared to be complicated in the case of malic dehydrogenase and fumarase.

The metabolism of mucopolysaccharides. 3. The effect of adrenocortical hormones on enzymes involved in glucuronide synthesis and metabolism in connective tissue.

The levels of activity of hexokinase, phosphoglucomutase, uridine diphosphoglucose pyrophosphorylase, and uridine diphosphoglucose dehydrogenase, which are involved in the synthesis of glucuronic acid, and the levels of glucuronosyltransferase and β-glucuronidase, which are involved in its metabolism, were studied in connective tissue from polyvinyl sponge implants from sham-operated and adrenalectomized rats which had received "replacement therapy" of individual steroids.The levels of activity of these enzymes were significantly increased in sham-operated rats which had been treated with corticosterone, cortisone, or hydrocortisone. In adrenalectomized animals, the increased or decreased enzyme activities were restored to normal levels by "therapy" with corticosterone, cortisone, or hydrocortisone. In some cases there was an over-correction at the particular level of hormone treatment. In both sham-operated and adrenalectomized animals, treatment with deoxycorticosterone, progesterone, or Reichstein's substance S frequently, but not always, resulted in little or no change in activity of the enzymes.

The metabolism of mucopolysaccharides. II. The effect of adrenalectomy on enzymes involved in glucuronide synthesis and metabolism in connective tissue.

The levels of activity of hexokinase, phosphoglucomutase, uridine diphosphoglucose pyrophosphorylase, and uridine diphosphoglucose dehydrogenase, which are involved in the synthesis of glucuronic acid, and the activities of glucuronosyl transferase and β-glucuronidase, which are involved in its metabolism, were studied in connective tissue from sham-operated and adrenalectomized rats. Adrenalectomy resulted in a significant decrease in phosphoglucomutase activity and in significant increases in the activities of hexokinase, uridine diphosphoglucose dehydrogenase, and β-glucuronidase. Adrenalectomy had no effect upon the activities of uridine diphosphoglucose pyrophosphorylase or glucuronosyl transferase.The added stress of either a sham injection or injection of sesame oil, both given daily and intraperitoneally, resulted in a significant increase in hexokinase activity and a decrease in glucuronosyl transferase and β-glucuronidase activities, in both sham-operated and adrenalectomized animals. The other enzymes were unaffected.

Purification of uridine diphosphoglucose dehydrogenase from calf liver

An improved procedure for purifying UDP-glucose dehydrogenase from calf liver was developed. This procedure is more reproducible and provides a better yield of a product with three times the specific activity of the best preparation previously described (1). Although some contaminating proteins are present in the final product, their sedimentation properties are sufficiently similar to that of UDP-glucose dehydrogenase to allow an estimation of its molecular weight, which is 3 × 10 5.

Histochemical Localization of Uridine Diphosphoglucose Dehydrogenase in Cartilage

THIS communication presents a method for the histochemical demonstration of uridine diphospho-glucose dehydrogenase in cartilage. This enzyme system is active in the pathway of synthesis of glucuronic acid1,2.

Interrelation of tryptophan and nicotinic acid in man during the first month of life.

IN the fœtal liver of mammals there is little or no activity of the following enzymatic systems : glucose-6-phosphatase1, uridine diphosphoglucose dehydrogenase, and glucuronyltransferase2, phenylalanine transaminase, tyrosine transaminase and phenylalanine hydroxylase3. Hence these enzymes reach the normal levels of activity during the first period of extra-uterine life, and for some of them it seems that this process is regulated or accelerated by the adrenocortical hormones.

Uridine diphosphoglucose dehydrogenase of pea seedlings.

Uridine diphosphoglucose dehydrogenase of pea seedlings.

Some properties of uridine diphosphoglucose dehydrogenase

Some aspects of the kinetics of uridine diphosphoglucose dehydrogenase have been studied. Thiosemicarbazide exerts a type of inhibition on the enzyme which indicates the presence of a carbonyl group on the catalytic site of the protein. The possibility of the dehydrogenase being one enzyme catalyzing both the oxidation steps involved in the conversion of uridine diphosphoglucose to uridine diphosphoglucuronic acid was discussed.