OBSERVATION ON THE CONFORMATIONAL CHANGE OF PHOSPHORYLASE ISOZYMES BY ELECTROFOCUSING

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Three isozymes of pig glycogen phosphorylase in the skeletal muscle, cardiac muscle and brain were studied mainly by means of electrofocusing. The isoelectric point of isozyme I, II and III located at pH 5.5, 5.9 and 6.35, respectively. Among these enzymes, isozyme III was found to be changed iso-electric point (pH 6.25) in contact with ammonium sulfate solution, and this changed protein appeared as a satellite-peak of native isozyme III peak. Pro-perties of the satellite-peak (isozyme III') were investigated comparing with native isozyme III. The results were as follows:(1) No difference on the catalytic properties between the two enzyme was observed except that specific activity of isozyme III' was lowered than that of isozyme III.(2) Isozyme III' still kept a dimer structure.(3) Isozyme III' could be converted to form "a" with phosphorylase kinase.(4) The reactivity of SH groups with DTNB was studied on both enzymes. It was shown that isozyme III' had one more reactive SH group per monomer which had been masked on the native enzyme.It was suggested from these results that conformational change occurred in the site which did not have significant effect on the active and ser-P sites.
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