Functional characteristics of hexokinase bound to the type a and type B sites of bovine brain mitochondria.
Hexokinase is released from Type A sites of brain mitochondria in the presence of glucose 6-phosphate (Glc-6-P); enzyme bound to Type B sites remains bound. Hexokinase of freshly isolated bovine brain mitochondria (Type A:Type B, approximately 40:60) selectively uses intramitochondrial ATP as substrate and is relatively insensitive to the competitive (vs ATP) inhibitor and Glc-6-P analog, 1,5-anhydroglucitol 6-phosphate (1,5-AnG-6-P). After removal of hexokinase bound at Type A sites, the remaining enzyme, bound at Type B sites, does not show selectivity for intramitochondrial ATP and has increased sensitivity to 1,5-AnG-6-P. Thus, the properties of the enzyme bound at Type B sites are modified by removal of hexokinase bound at Type A sites. It is suggested that mechanisms for regulation of mitochondrial hexokinase activity, and thereby cerebral glycolytic metabolism, may depend on the ratio of Type A:Type B sites, which varies in different species.
de Cerqueira Cesar
Marcelo
M
Departamento de Ciencias Basicas, Universidade de São Paulo, 13630-970, Pirassununga, SP, Brazil.
Wilson
John E
JE
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D005695:Galactosephosphates / Q000378:metabolism; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006593:Hexokinase / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008928:Mitochondria / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D051381:Rats; D013053:Spectrophotometry
D005695:Galactosephosphates; D019298:Glucose-6-Phosphate; C038269:galactose-6-phosphate; D000255:Adenosine Triphosphate; D006593:Hexokinase; D010100:Oxygen