Regulation of glutaminase B in Escherichia coli. I. Purification, properties, and cold lability.
Escherichia coli contains two glutaminases, A and B, with pH optima below pH 5 and above pH 7, respectively. Neither glutaminase A nor B is released from E. coli by osmotic shock. Glutaminase B has been purified 6,000-fold and the purified preparation is estimated to contain about 40% glutaminase B. The enzyme has a molecular weight of 90,000 and an isoelectric point of 5.4. Glutaminase B exhibits a broad pH optimum between 7.1 and 9.0. Only L-glutamine is deamidated by glutaminase B, L-asparagine and D-glutamine are not deamidated. The substrate saturation curve for glutaminase B shows an intermediary plateau region. Like many regulatory enzymes, glutaminase B is cold-labile. The enzyme is inactivated by cooling and activated by warming; both processes are first order with respect to time. The activation energy for activation by warming was calculated to be 5900 cal/mol. Activation by warming increased the Vmax and decreased the S0.5 for L-glutamine, but did not alter the molecular weight of the catalytically active enzyme. Borate and glutamate protected glutaminase B from inactivation by cold.
D003080:Cold Temperature; D004355:Drug Stability; D004926:Escherichia coli / Q000201:enzymology*; D005972:Glutaminase / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors
D007527:Isoenzymes; D005972:Glutaminase