Histone II-A stimulates glucose-6-phosphatase and reveals mannose-6-phosphatase activities without permeabilization of liver microsomes.
The effect of histone II-A on glucose-6-phosphatase and mannose-6-phosphatase activities was investigated in relation to microsomal membrane permeability. It was found that glucose-6-phosphatase activity in histone II-A-pretreated liver microsomes was stimulated to the same extent as in detergent-permeabilized microsomes, and that the substrate specificity of the enzyme for glucose 6-phosphate was lost in histone II-A-pretreated microsomes, as [U-14C]glucose-6-phosphate hydrolysis was inhibited by mannose 6-phosphate and [U-14C]mannose 6-phosphate hydrolysis was increased. The accumulation of [U-14C]glucose from [U-14C]glucose 6-phosphate into untreated microsomes was completely abolished in detergent-treated vesicles, but was increased in histone II-A-treated microsomes, accounting for the increased glucose-6-phosphatase activity, and demonstrating that the microsomal membrane was still intact. The stimulation of glucose-6-phosphatase and mannose-6-phosphatase activities by histone II-A was found to be reversed by EGTA. It is concluded that the effects of histone II-A on glucose-6-phosphatase and mannose-6-phosphatase are not caused by the permeabilization of the microsomal membrane. The measurement of mannose-6-phosphatase latency to evaluate the intactness of the vesicles is therefore inappropriate.
St-Denis
J F
JF
Department of Nutrition, Université de Montréal, Québec, Canada.
Annabi
B
B
Khoury
H
H
van de Werve
G
G
D000818:Animals; D002793:Cholic Acids; D003902:Detergents; D004789:Enzyme Activation; D005952:Glucose-6-Phosphatase / Q000378:metabolism*; D006657:Histones / Q000494:pharmacology*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D002793:Cholic Acids; D003902:Detergents; D006657:Histones; C048531:chapso; C023553:mannose-6-phosphatase; D010744:Phosphoric Monoester Hydrolases; D005952:Glucose-6-Phosphatase