The majority of vitamin B6 in the body is in skeletal muscle, bound as the cofactor pyridoxal 5'-phosphate to one abundant protein, glycogen phosphorylase. Previous work has established that radiolabelled vitamin B6 can be used as a turnover label for glycogen phosphorylase. In this study, a stable isotope derivative of pyridoxine {dideuterated pyridoxine; 3-hydroxy-4-(hydroxymethyl) -5-[hydrox...

CP320626, a potential antidiabetic drug, inhibits glycogen phosphorylase in synergism with glucose. To elucidate the structural basis of synergistic inhibition, we determined the structure of muscle glycogen phosphorylase b (MGPb) complexed with both glucose and CP320626 at 1.76 A resolution, and refined to a crystallographic R value of 0.211 (R(free)=0.235). CP320626 binds at a novel allosteri...

The two examples of phospho and dephospho proteins for which structural data were previously available (glycogen phosphorylase and isocitrate dehydrogenase) demonstrated two different mechanisms for control. In glycogen phosphorylase, activation by phosphorylation results in long-range allosteric changes. In isocitrate dehydrogenase, inhibition by phosphorylation is achieved by an electrostatic...

The wood frog, Rana sylvatica, from Interior Alaska survives freezing at -16°C, a temperature 10-13°C below that tolerated by its southern conspecifics. We investigated the hepatic freezing response in this northern phenotype to determine if its profound freeze tolerance is associated with an enhanced glucosic cryoprotectant system. Alaskan frogs had a larger liver glycogen reserve that was mob...

A phosphatase, active towards phosphorylase a and phosphorylated proteins casein and histone II-A, was isolated from Saccharomyces cerevisiae 257. The enzyme dephosphorylated glycogen phosphorylase from commercial yeast rendering it inactive. The protein phosphatase activity was not influenced by any metal ions. Phosphorylase phosphatase activity was slightly stimulated by p-nitrophenyl phospha...

This study was initiated to determine whether glycogen phosphorylase activation was defective in hearts of alloxan diabetic rats. When hearts were perfused by gravity flow for 1 to 10 min with various concentrations of epinephrine, activation of glycogen phosphorylase in the diabetic was significantly greater at every time and epinephrine concentration than that seen in the normal. Cyclic AMP a...

Vanadate inactivated rat hepatocyte glycogen synthase and activated glycogen phosphorylase in a dose- and time-dependent manner. These effects were observed in hepatocytes from both fasted as well as fed rats. When rat hepatocytes were preincubated with [32P]phosphate and then with vanadate, and the 32P-labeled glycogen synthase was specifically immunoprecipitated, it was observed that vanadate...

..................................... 5 Introduction................................ 9 1.1 The fat body ................................................................... 9 1.2 The adipokinetic hormones .......................................... 9 1.3 Glycogen phosphorylase ............................................. 10 1.4 The role of cyclic AMP ................................................

The activity of phosphorylase in muscle appears to regulate glycogenolysis (1, 2). The enzyme has been found to exist in two forms, a and b (3-5). Phosphorylase b is active only in the presence of adenosine 5’-monophosphate, whereas phosphorylase a is active in the absence of the nucleotide. Epinephrine and other catecholamines are known to increase phosphorylase activity by accelerating conver...

Liver glycogen phosphorylase kinase was assayed by measuring the radioactivity of [y-32P]ATP incorporated into rabbit skeletal muscle phosphorylase b. Using this assay two forms of phosphorylase kinase, Kinase I and Kinase II, were pirified about 70and 130-fold, respectively, from rabbit liver cytosol by DEAE-Sephadex A50 column chromatography, ammonium sulfate fractionation, gel filtration on ...