Relationship between microsomal membrane permeability and the inhibition of hepatic glucose-6-phosphatase by pyridoxal phosphate.
Arion et al; (Arion, W. J., Wallin, B. K., Lange A. J., and Ballas, L. M. (1975) Mol. Cell. Biochem. 6, 75-83) propsed a model for glucose-6-phosphatase in which the substrate was transported across the microsomal membrane by a carrier before hydrolysis on the cisternal side. Evidence to support this model has been obtained by studying the inhibition of the enzyme by pyridoxal-P. Pyridoxal-P was a linear noncompetitive inhibitor of glucose-6-phosphatase (EC 3.1.3.9) in freshly isolated ("intact") microsomes from rat liver. Pyridoxol-P was a much less effective inhibitor and no inhibition was observed with pyridoxamine-P. When microsomes were subjected to nitrogen cavitation, treatment with solium deoxycholate, or glutaraldehyde fixation, the Km of glucose-6-phosphatase for glucose-6 P decreased from approximately 6 mM to approximately 2.5 mM; the corresponding change in the Vmax ranged from-10% to +40%. The same procedures decreased the inhibition of glucose-6-phosphatase by pyridoxal-P several-fold. No inhibition by pyridoxal-P was observed in a preparation of glucose-6-phosphatase purified approximately 20 fold (on the basis of Vmax) from micoromes. A nondialyzable inhibitor was apparently formed when intact microsomes were reacted with pyridoxal-P and NaBH4; this inhibition was also reversed by procedures which changed the kinetic properties of glucose-6-phosphatase.
D000818:Animals; D001692:Biological Transport; D001894:Borohydrides / Q000494:pharmacology; D004492:Edetic Acid / Q000378:metabolism; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008954:Models, Biological; D010539:Permeability; D011732:Pyridoxal Phosphate / Q000494:pharmacology*; D051381:Rats
D001894:Borohydrides; D011732:Pyridoxal Phosphate; D004492:Edetic Acid; D005952:Glucose-6-Phosphatase