Nov 10, 1976

Quantitative aspects of relationship between glucose 6-phosphate transport and hydrolysis for liver microsomal glucose-6-phosphatase system. Selective thermal inactivation of catalytic component in situ at acid pH

The Journal of Biological Chemistry
W J ArionL M Ballas


Studies of the thermal stability of rat liver glucose-6-phosphatase (EC were carried out to further elevate the proposal that the enzymic activity is the result of the coupling of a glucose-6-P-specific translocase and a nonspecific phosphohydrolase-phosphotransferase. Inactivation was observed when micorsomes were incubated at mild temperatures between pH 6.2 and 5.6. The rate of inactivation increased either with increasing hydrogen ion concentration or temperature. However, no inactivation was seen below 15 degrees in media as low as pH 5 or at neutral pH up to 37 degrees. The thermal stability of the enzyme may be controlled by the physical state of the membrane lipids and the degree of protonation of specific residues in the enzyme protein. Microsomes were exposed to inactivating conditions, and kinetic analyses were made of the glucose-6-P phosphohydrolase activities before and after supplementation to 0.4% sodium taurocholate. The results support the postulate and the kinetic characteristics of a given preparation of intact microsomes are determined by the relative capacities of the transport and catalytic components. Before detergent treatment, inactivation (i.e. a decrease in Vmax) was accompanied by a decreas...Continue Reading

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Mentioned in this Paper

Microsomal Membrane
Hydrogen Ion Concentration Measurement
Depressed - Symptom
Phosphate Ion Transport
Phosphate Measurement
Microsomes, Liver

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