Date of Award

1-1-1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry

Abstract

Net glucose uptake was studied in isolated perfused livers from fed and fasted rates in the presence of discriminant inhibitors of enzymes responsible for glucose phosphorylation. N-Acetyl-glucosamine, a potent inhibitor of glucokinase and hexokinase, significantly inhibited net glucose uptake in livers from fed but not fasted rats. This result could not be explained if glucokinase and hexokinase were the only enzymes responsible for glucose phosphorylation in the fasted state. Under some conditions glucose uptake was inibited by 3-O-methylglucose and by ornithine. Both of these compounds are inhibitors of glucose phosphorylation via the phosphotransferase activity of glucose-6-phosphatase but have no effect on the activity of glucokinase or hexokinase. Perfused livers from fed, fasted and diabetic rats converted 3-O-methylglucose to a negatively charged product (presumably 3-O-methylglucose-6-P) in the absence of exogenously supplied phosphoryl donor. All of the above support the proposed role of glucose-6-phosphatase phosphotransferase as an auxiliary mechanism for glucose phosphorylation in rat liver.Glycogen deposition and glucose-6-P levels were studied in perfused livers from fasted and fed rats as a function of glucose concentration. The increase in hepatic glucose-6-P seen in response to a glucose load is compatible with the involvement of a high K(,m) glucose phosphorylating enzyme in addition to glucokinase in the flux from glucose to hepatic glycogen.

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