Kaur J, Jaswal V M, Mahmood A
Department of Biochemistry, Panjab University, Chandigarh, India.
Indian J Exp Biol. 1990 Jan;28(1):18-22.
Administration of cortisone and thyroxine produced adult-type increase in the activities of soluble and membrane-bound gamma-glutamyltranspeptidase (gamma-GTP) in suckling rat intestine. Membrane-bound enzyme activity remained unaltered while the soluble enzyme activity was reduced (27%) in insulin-injected pups. Kinetic analysis revealed that the observed changes in the enzyme levels were a consequence of altered Vmax with no change in apparent Km. A 2-fold increase in the Km value was observed in adult gamma-GTP activity compared to that of suckling animals. Membrane-bound and soluble gamma-GTP yielded similar values of the Ea (9.7-13.1 kcal/mole) but exhibited apparent differences in heat stability in the control and hormone-injected groups. Leucine-amino peptidase(LAP) activity was reduced to adult levels in insulin-treated suckling animals. Thyroxine- and cortisone-treatment did not affect soluble activity but significantly (P less than 0.001) augmented the membrane-bound LAP levels. This increase was due to enhanced (54-82%) Vmax with no change in Km. The observed decrease in LAP activity in response to insulin was due to reduced Vmax. There was no change in Ea (8-11.6 kcal/mole) except the value was raised to 19.1 kcal/mole in cortisone-injected pups. Both the soluble and membrane-bound LAP activities were quite resistant to heat inactivation upto 30 min at 60 degrees C except in weanling rats. Thus, the kinetic behaviour of normally developed and precociously induced gamma-GTP and LAP is essentially similar but there are apparent differences in the mode of action of insulin, cortisone and thyroxine in affecting the development of these enzymes.
给乳鼠注射可的松和甲状腺素后，其小肠中可溶性和膜结合型γ-谷氨酰转肽酶（γ-GTP）的活性出现成年型增加。胰岛素注射的幼鼠中，膜结合型酶活性保持不变，而可溶性酶活性降低了27%。动力学分析表明，观察到的酶水平变化是Vmax改变的结果，表观Km没有变化。与乳鼠相比，成年γ-GTP活性的Km值增加了2倍。膜结合型和可溶性γ-GTP的Ea值相似（9.7-13.1千卡/摩尔），但在对照组和激素注射组中，其热稳定性存在明显差异。胰岛素处理的乳鼠中，亮氨酸氨基肽酶（LAP）活性降至成年水平。甲状腺素和可的松处理不影响可溶性活性，但显著（P<0.001）提高了膜结合型LAP水平。这种增加是由于Vmax增强（54-82%），而Km不变。观察到的胰岛素导致LAP活性降低是由于Vmax降低。Ea没有变化（8-11.6千卡/摩尔），但可的松注射的幼鼠中Ea值升至19.1千卡/摩尔。除了断奶大鼠外，可溶性和膜结合型LAP活性在60℃下长达30分钟都对热失活具有相当的抗性。因此，正常发育和早熟诱导的γ-GTP和LAP的动力学行为基本相似，但胰岛素、可的松和甲状腺素在影响这些酶发育方面的作用方式存在明显差异。
