Kinetic properties of gamma-glutamyltranspeptidase and leucine-amino-peptidase in developing rat intestine: effect of hormones.
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.
Kaur
J
J
Department of Biochemistry, Panjab University, Chandigarh, India.
Jaswal
V M
VM
Mahmood
A
A
D000818:Animals; D000833:Animals, Suckling; D003348:Cortisone / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology*; D007422:Intestines / Q000201:enzymology* / Q000254:growth & development; D007700:Kinetics; D007931:Leucyl Aminopeptidase / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013974:Thyroxine / Q000494:pharmacology; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D006728:Hormones; D005723:gamma-Glutamyltransferase; D007931:Leucyl Aminopeptidase; D013974:Thyroxine; D003348:Cortisone