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Phosphate‐Activated Glutaminase in the Crude Mitochondrial Fraction (P2 Fraction) from Human Brain Cortex
Author(s) -
Svenneby Gerd,
Roberg Bjørg,
Hogstad Svein,
Torgner Ingeborg Aa.,
Kvamme Elling
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb00764.x
Subject(s) - glutaminase , phosphate , enzyme , biochemistry , glutamine , glutamate receptor , chemistry , activator (genetics) , substrate (aquarium) , enzyme assay , carbamoyl phosphate synthetase , biology , amino acid , ecology , receptor , gene
The kinetics and other properties of phosphate‐activated glutaminase have for the first time been studied in the crude mitochondrial fraction (P2 fraction) from human brain. The enzyme is for unexplained reasons inactivated postmortem. The enzyme activity decreases by storing the tissue or homogenate at 37°. The inactivation is not caused by formation of a dialysable inhibiting compound. No large proteolytic degradation has occurred, since the phosphate‐activated glutaminase‐like immunoreactive band did not disappear during the storage. The molecular weight of the subunit of the enzyme as determined by immunoblots of sodium dodecyl sulfate‐treated homogenates from human brain is estimated to be approximately 64 K. The enzyme has been shown to have a pH optimum of 8.6; it is activated by phosphate, inhibited by glutamate, and partially inhibited by ammonia. Double‐inverse plots of enzyme activity against phosphate are concave‐upward, and more so in the presence of an inhibitor. The inhibition by glutamate ap pears to be noncompetitive with the substrate glutamine, and competitive with the activator phosphate. These kinetic properties are not significantly different from our earlier observations concerning phosphate‐activated glutaminase from pig brain and pig kidney.