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PubMed1986

Tissue uridine pools: evidence in vivo of a concentrative mechanism for uridine uptake.

Pools of free uridine, ranging from 7.3 to 38.0 nmol/g wet weight, have been detected in a variety of freeze-clamped murine tissues. These concentrations average 10-fold greater than that detected in plasma. The kinetics of these pools after an i.v. tracer dose of [3H]uridine suggest that the initial rapid disappearance of [3H]uridine from plasma (t1/2 = 2 min) reflects distribution into tissues as well as catabolism by the liver. Subsequently, the tissue uridine pools turn over with half-lives of 13 to 18 h. Analyses of the activity of the proximal enzymes in uridine metabolism (uridine phosphorylase and uridine kinase) suggest that the phosphorylase correlates with the size of tissue uridine pools. Further evidence for this is seen in the sustained 5- to 15-fold increase in both tissue and plasma uridine concentrations after treatment with benzylacyclouridine, a potent uridine phosphorylase inhibitor. In contrast, a nonphysiological dose of exogenous uridine (250 mg/kg) briefly increases the plasma concentration of uridine to over 1 mM but it returns to below 10 microM within 1 h. Under these conditions as well, tissue concentrations of uridine increase 5- to 10-fold in most tissues, 20-fold in spleen, and 70-fold in kidney. High cellular concentrations of free uridine relative to medium are also observed in dispersed murine splenocytes. Furthermore, splenocytes incubated in 5 microM [3H]uridine achieved a 2-fold higher intracellular concentration of [3H]uridine in less than 1 min independent of phosphorylation. Thymidine was not concentrated in this system nor did nitrobenzylthioinosine inhibit [3H]uridine uptake. These findings suggest that in normal tissues and explanted cells, pools of uridine are sustained by a concentrative transport mechanism and constitute a previously unrecognized reservoir of pyrimidine nucleosides in tissues.

Animals↗
PubMed1973

Phosphorylation of the "37000 component" of the troponin complex (troponin-t).

Most of the phosphorus present in the troponin complex, which on average contains 1 mol of P/80000g, is associated with the ;37000 component' (0.6mol of P/mol). The inhibitory protein and particularly the ;37000 component', but not the calcium-binding protein, were phosphorylated when incubated with phosphorylase b kinase and [gamma-(32)P]ATP.

Animals↗
PubMed1985

Phosphorylase phosphatase and phosphatase activating-kinase FA in growing rat muscles.

The activities of phosphorylase phosphatase and of FA, the kinase that activates phosphatase, were measured in rat skeletal muscle from birth to 200 g body weight. Throughout this period part of phosphatase was always spontaneously active. The activity could be further increased by trypsin, but did not additionally increase when Mn2+ was present. During the first 15-20 days of life most of the phosphatase was cytosolic. Then it decreased in this fraction and more phosphatase was found in glycogen particles, to reach the adult level at about 50 g body weight. Also the activity of the kinase FA was lower for the first 10 days, then it increased attaining the adult level again at about 50 g. These results are compared to those on phosphorylase activity and glycogen level in muscle and on serum insulin during growth.

Aging↗
PubMed1975

Purification and characterization of a phosphoprotein phosphatase from bovine adrenal cortex.

A phosphoprotein phosphatase which is active against chemically phosphorylated protamine has been purified about 500-fold from bovine adrenal cortex. The enzyme has a pH optimum between 7.5 and 8.0, and has an apparent Km for phosphoprotamine of about 50 muM. The hydrolysis of phosphoprotamine is stimulated by salt, and by Mn2+. Hydrolysis of phosphoprotamine is inhibited by ATP, ADP, AMP, and Pi, but is not affected by AMP or cyclic GMP. The purified phosphoprotein phosphatase preparation also dephosphorylates p-nitrophenyl phosphate and phosphohistone, and catalyzes the inactivation of liver phosphorylase, the inactivation of muscle phosphorylase a (and its conversion to phosphorylase b), and the inactivation of muscle phosphorylase b kinase. Phosphatase activities against phosphoprotamine and muscle phosphorylase a copurify over the last three stages of purification. Phosphoprotamine inhibits phosphorylase phosphatase activity, and muscle phosphorylase a inhibits the dephosphorylation of phosphoprotamine. These results suggest that one enzyme possesses both phosphoprotamine phosphatase and phosphorylase phosphatase activities. The stimulation of phosphorylase phosphatase activity, but not of phosphoprotamine phosphatase activity, by caffeine and by glucose, suggests that the different activities of this phosphoprotein phosphatase may be regulated separately.

Adenine Nucleotides↗
PubMedDate not supplied

[Regularities of organ-specific expression of enzyme systems in cattle].

The organ specificity of creatine kinase, esterase, isocitrate dehydrogenase lactate dehydrogenase, nucleoside phosphorylase, adenylate kinase, hexokinase, malate dehydrogenase, malic enzyme, glucose-6-phosphate dehydrogenase of black-white cattle has been studied. Esterases, creatine kinase, adenylate kinase, hexokinase and glucose-6-phosphate dehydrogenase have a very wide spectrum of the organ variabilities. Liver and heart have the largest specificity of enzymes activity. Some peculiarities of isozyme spectrum are found in ovaries and spleen.

Adenylate Kinase↗