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At least 415 records · Page 23Linked to original sources
PubMed1994

Clinical and biochemical features of 10 adult patients with muscle phosphorylase kinase deficiency.

Ten adult patients complained of exercise intolerance; five of them had cramps and three had recurrent myoglobinuria. Resting serum CK was increased in five. Muscle biopsies showed phosphorylase b kinase (PbK) deficiency, whereas the activities of other enzymes of carbohydrate metabolism were normal. None of the patients exhibited symptoms indicative of liver PbK deficiency. Thus, these patients are new additions to a class of PbK glycogen storage disease characterized by enzyme deficiency in muscle but not liver. Family histories were consistent with autosomal recessive transmission. Monoclonal antibodies specific for the beta and gamma subunits of PbK cross-reacted differentially with muscle biopsies from three of these patients, suggesting that this phenotype of PbK deficiency is biochemically heterogeneous.

Adolescent↗
PubMed1999

Phosphorylase kinase: the complexity of its regulation is reflected in the complexity of its structure.

Intracellular glycogen stores are used to maintain blood-glucose homeostasis during fasting, are a source of energy for muscle contraction, and are used to support a broad range of cellular activities in most tissues. A diversity of signals accelerate glycogen degradation that are mediated by phosphorylase b kinase (Phk), which phosphorylates and thereby activates glycogen phosphorylase. Phk is among the most complex of the protein kinases so far elucidated. It has one catalytic (gamma) subunit and three different regulatory (alpha, beta, and delta) subunits, a molecular mass of 1.3 X 106 daltons, and each holoenzyme molecule is presumed to contain four molecules of each subunit. The three regulatory subunits inhibit the phosphotransferase activity of the gamma subunit. Ca2+ relieves inhibition via the delta subunit, which is identical to calmodulin but remains an integral component of the holoenzyme even when the [Ca2+] is lowered to nanomolar levels. Phosphorylation of the alpha and beta subunits by the 3',5'-cyclic adenosine monophosphate (cAMP)-dependent protein kinase (PKA) also relieves inhibition of the gamma subunit and thereby activates the enzyme. The stimulatory effects of Ca2+ and phosphorylation appear to be structurally coupled and are cooperative. In addition, Phk is activated in vitro by autophosphorylation, limited proteolysis of the regulatory subunits, and various allosteric effectors and these may also be mechanisms of physiological importance. The molecular mechanisms of regulation are currently poorly understood, but new insights are beginning to emerge. This review discusses current knowledge and concepts of the structure, function and regulation of Phk.

Amino Acid Sequence↗
PubMedDate not supplied

[Effect of temperature on the kinetics of the phosphorylase reaction and phosphorylase activation induced by phosphorylase kinase in the skate Dasyatis pastinaca].

The dependence of the phosphorylation reaction rate on the glucose-1-phosphate concentration is investigated in Dasyatis pastinaca in a wide temperature range (5-45 degrees C). In the temperature range of 20-40 degrees C nH is equal to 1.3-1.7. The disturbance of allosteric interactions of active sites with the loss of kinetic substrate cooperativity is observed at 45 degrees C. v(S)-Dependence with the intermediate plateau is obtained at 5 degrees C and high concentration of glycogen phosphorylase B (EC 2.4.1.1), that is explained by the formation of inactive tetramer. Studies in activation of glycogen phosphorylase B of Dasyatis pastinaca under the effect of glycogen phosphorylase (EC 2.7.1.38) kinase have revealed temperature-dependent changes in the pattern of kinetic curve. An assumption is advanced that the presence of the association-dissociation equilibrium in oligomeric forms of glycogen phosphorylase B with different enzymic activity and the effect of the temperature-dependent conformation state of this enzyme on the kinase reaction rate plays an essential role in regulation of glycogenolysis in the muscular tissue of ectothermal animals.

Animals↗