Interaction of mannose-6-phosphate with the hysteretic transition in glucose-6-phosphate hydrolysis in intact liver microsomes.
We showed previously that glucose-6-phosphatase activity was characterised in intact liver microsomes by a hysteretic transition between a rapid and a slower catalytic form of the enzyme. We have now further investigated the substrate specificity of these two kinetic forms. It was found that the pre-incubation of intact microsomes with mannose-6-phosphate or glucose-6-phosphate (50 microM for 30 s) suppressed the burst in glucose-6-phosphatase activity, that the hysteretic transition was reversible and that mannose-6-phosphate inhibited glucose-6-phosphate hydrolysis during the first seconds of incubation, but not anymore after the burst. Our results indicate (i) that mannose-6-phosphate is recognised by the enzyme and can promote the hysteretic transition and (ii) that the transient phase is part of the catalytic mechanism itself.
Vidal
H
H
Department of Nutrition, University of Montreal, Que., Canada.
Berteloot
A
A
Larue
M J
MJ
St-Denis
J F
JF
van de Werve
G
G
D000818:Animals; D002384:Catalysis; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism* / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D008360:Mannosephosphates / Q000378:metabolism* / Q000494:pharmacology; D008862:Microsomes, Liver / Q000201:enzymology; D051381:Rats; D013379:Substrate Specificity
D005958:Glucosephosphates; D008360:Mannosephosphates; C027693:mannose-6-phosphate; D019298:Glucose-6-Phosphate; D005952:Glucose-6-Phosphatase