Glycogenesis and glyconeogenesis in human platelets: Incorporation of glucose, pyruvate, and citrate into platelet glycogen; glycogen synthetase and fructose-1,6-diphosphatase activity

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Abstract

Washed human platelets are capable of depositing 1-4 as well as probable 1-6 glucosyl linkages onto preexistent glycogen primer. They are also capable of degrading (glycogenolysis) newly synthesized 1-4 as well as probable 1-6 glucosyl linkages. A higher rate of glycogen synthesis was found in platelet suspensions containing lower concentrations of platelets. This was shown to result from decreased glycogen degradation and consequent increased residual glycogen primer in low platelet suspensions. The increased glycogen content of low platelet suspensions was not a result of platelet washing, removal of platelets from plasma, or release of platelet metabolites into the media. The enzyme glycogen synthetase was found to be present at a rate of 5.2 μmoles of uridine diphosphate (UDP) glucose incorporated into glycogen per gram platelets per hour at 37°C. The Km for UDP glucose was 6.6 mmoles/liter. At optimum concentration of glucose 6-phosphate, the Km was reduced 4.6 fold and Vmax was increased 4.3-fold.

Authors

Simon Karpatkin, Arthur Charmatz, Richard M. Langer