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G Bot

Publications and source records attributed to G Bot.

70 records · Page 4Linked to original sources
PubMed1977

Role of tetramer in equilibrium dimer equilibrium in the dephosphorylation and activity of phosphorylase a.

Skeletal muscle phosphorylase a exists as a tetramer or a dimer depending upon the temperature and protein concentration. The rate of dephosphorylation by phosphorylase phosphatase is very low at 18 degrees C where phosphorylase a exists as a tetramer. Caffeine markedly increases the rate of dephosphorylation of tetrameric phosphorylase a at 18 degrees C but has no effect on the dephosphorylation of the dimeric form. Caffeine also enhances the enzymic activity of phosphorylase a at 18 degrees C. The results presented here indicate that caffeine can shift the tetramer in equilibrium dimer equilibrium toward the dimeric form at 18 degrees C. This conclusion in supported by sedimentation analyses.

Caffeine↗
PubMed1976

Thiophosphate-activated phosphorylase kinase as a probe in the regulation of phosphorylase phosphatase.

Rabbit muscle nonactivated phosphorylase kinase (EC 2.7.1.38) is converted to thiophosphate-activated phosphorylase kinase by cyclic AMP dependent protein kinase, Mg2+ and ATP-gamma-S/adenosine-5'-O-(s-thiotriphosphate)/. The formation of thiophosphate-activated phosphorylase kinase wal also observed in the protein-glycogen complex from skeletal muscle. This new form of kinase is resistant to the action of phosphatase and behaves as a competitive inhibitor in the dephosphorylation of phosphorylase alpha by phosphorylase phosphatase (Ki = 0.04 mg per ml). The fact that the inhibitory effect of thiophosphate-activated phosphorylase kinase is 3 times higher than in the case of nonactivated kinase, may explain the transient inhibition of phosphorylase phosphatase in the protein-glycogen complex. The use of activated (phosphorylated) phosphorylase kinase supports this assumption since it causes a delay in the dephosphorylation of phosphorylase alpha, i.e. the conversion of phosphorylase alpha into beta could start only after the dephosphorylation of activated phosphorylase kinase.

Adenosine Triphosphate↗
PubMed1975

Properties of skeletal muscle phosphorylase-protein complexes.

Frontal gel filtration studies on muscle extract and mixture of purified enzymes have verified the existence of a protein-complex between phosphorylase (alpha-1,4-glucan: orthophosphate glycosyltransferase EC 2.4.1.1.) and phosphorylase kinase. The complex has an apparent molecular weight of 750 000 daltons. The complex formation depends on the protein concentration and the presence of Ca2+. Removal of Ca2+ with EGTA results in the dissociation of the complex. A regulatory role may be attributed to Ca2+ since the concentration of free Ca2+ changes in skeletal muscle through the effect of hormonal or electrical stimulation. Strong association was also detected between phosphorylase kinase and phosphorylase phosphatase. The transient inhibition of phosphorylase phosphatase can be explained by this interaction.

Animals↗
PubMedDate not supplied

Protecting effects of intravenous insoluble glycogen treatment on the experimental necrotizing acute pancreatitis of dogs.

BACKGROUND/AIMS: We have studied the effects of insoluble glycogen applied intravenously on the experimental acute pancreatitis of dogs. METHODS: Experimental acute pancreatitis was induced by olive oil injected into the main pancreatic duct. The effects of insoluble glycogen were evaluated histologically and by measurements of levels of amylase, lipase in sera. The binding of endotoxin and secretable phospholipase A2 by insoluble glycogen were tested by isotopically labeled materials. RESULTS: Application of insoluble glycogen had beneficial effects on the experimental acute pancreatitis of dogs. CONCLUSION: The binding capacity on endotoxin and secretable phospholipase A2 could play the main role in the protection offered by insoluble glycogen.

Amylases↗