PMID: 6411704Aug 25, 1983Paper

Endogenous phosphates on liver glycogen synthase D and synthase I. Studies on the number and location.

The Journal of Biological Chemistry
A W Tan, F Q Nuttall

Abstract

Synthase D and synthase I of high specific activity have been isolated from rabbit liver, with subunit Mr = 78,000 and 85,000, respectively. Minor bands of Mr = 78,000 and 71,000 were also observed, and these were shown to be proteolytic products containing synthase activity. Incubation with trypsin resulted in no activity changes, but there was a conversion of synthase I to the Mr = 78,000 species. Incubation with chymotrypsin produced no change in total synthase activity, but both enzymes were converted to the Mr = 71,000 species. Synthase I, after chymotrypsin treatment, became dependent on glucose-6-P for activity. Kinetic studies indicated that the chymotrypsin-treated synthase D and synthase I were not the same species. Synthase D contained 5.7 mol of alkali-labile phosphate/subunit and synthase I, 2.9 mol/subunit. With trypsin treatment there was little loss of phosphate from synthase. With chymotrypsin treatment, there was a loss of 3.1 and 1.5 mol of phosphate/subunit from synthase D and I, respectively. Some conversion to synthase I still occurred when chymotrypsin-treated synthase D was incubated with crude extract, suggesting that the phosphates which remained were still removable by synthase phosphatase. The presen...Continue Reading

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