Allosteric regulation of liver phosphorylase a: revisited under approximated physiological conditions

Archives of Biochemistry and Biophysics
N ErcanFrank Q Nuttall

Abstract

Phosphorylase removes glucosyl units from the terminal branches of glycogen through phosphorolysis, forming glucose-1-P. It is present in two interconvertible forms, phosphorylase a and b. The a form is the active form and is rate limiting in glycogen degradation. The activities of phosphorylase a and of total phosphorylase as conventionally measured exceed the activities of glycogen synthase R (active form) and of total synthase by approximately 10- and 20-fold. Thus, unless phosphorylase a is inhibited or compartmentalized or its substrates are exceedingly low in vivo, net glycogen synthesis could not occur. In addition, following an administered dose of glucose, phosphorylase a activity changes little when glycogen is being synthesized, is stable, or is being degraded, suggesting an important role for allosteric effectors in regulation. Therefore, we have determined the effect of potential modifiers of enzyme activity at estimated intracellular concentrations. Purified liver phosphorylase a was used. Activity was measured in the direction of glycogenolysis, at 37 degrees C, pH 7.0, and under initial rate conditions. Both a Km and a near-saturating concentration of inorganic phosphate (substrate) were used in the assays. A ph...Continue Reading

References

Oct 17, 2009·Journal of Biological Physics·Dirk Langemann, Marcel Rehberg
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Oct 14, 2008·BMC Physiology·Marie-Christine BeauvieuxJean-Louis Gallis
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Mar 1, 2018·The Journal of Biological Chemistry·J Scott LeeSean P Colgan
Mar 31, 2005·American Journal of Physiology. Endocrinology and Metabolism·Nacide Ercan-FangFrank Q Nuttall
Jun 19, 2008·Diabetes/metabolism Research and Reviews·Frank Q NuttallMary C Gannon
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Feb 13, 2001·American Journal of Physiology. Endocrinology and Metabolism·Nacide Ercan-FangMary C Gannon
Jun 18, 2002·American Journal of Physiology. Endocrinology and Metabolism·Nacide Ercan-FangFrank Q Nuttall

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