Date of Award

1-1-1982

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biochemistry

Abstract

Studies of the effects of micromolar concentrations of a variety of di- and trivalent cations on glucokinase and hexokinase activities of rat liver found potent inhibition of both enzymes by Cu('+2) or Cr('+3). As determined by the Dixon and the Cornish-Bowden graphical methods of analysis for enzyme inhibition, Cr('+3) was a mixed inhibitor of glucokinase when either D-glucose or ATP and MgCl(,2) are the substrates varied and Cu('+2) was a competitive inhibitor of gluokinase when D-glucose is the substrate varied.The preference of glucose-6-phosphatase to catalyze glucose-6-P hydrolysis via the glucose-6-P phosphohydrolase reaction was compared to its synthesis via the phosphotransferase activities. Also, the preference to utilize carbamyl-P compared to glucose-6-P as phosphoryl donor in the phosphotransferase catalyzed reactions was studied. These comparisons for untreated and deoxycholate treated enzyme preparations as well as additional single- and two-substrate kinetic studies at pH 7 for glucose-6-P phosphohydrolase and several phosphotransferase activities indicated that the phosphotransferase activities have the potential for being physiologically functional. Also, carbamyl-P and glucose-6-P can both effectively function as substrates for the enzyme of intact as well as detergent-treated microsomes. From the kinetic studies, the Michaelis constants for both glucose-6-P and carbamyl-P in the phosphotransferase catalyzed reaction and for glucose-6-P phosphohydrolase were significantly lower for detergent-treated compared to intact microsomes. One explanation of the decrease in the Michaelis constant for glucose-6-P which occurs upon detergent treatment involved the presence of transport proteins specific for glucose-6-P. Then, on this basis, if there are transporters for glucose-6-P, there must be transporters for carbamyl-P.

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