Kinetic comparison of rat pulmonary and renal gamma-glutamyl transpeptidase activities.

Glutathione (GSH) protects the lung against oxidative injury from environmental pollutants. gamma-Glutamyl transpeptidase (GGT) plays an integral role in the utilization and degradation of glutathione. Although GGT has been extensively studied in the kidney, little is known about GGT activity in the lung. This study compares pulmonary and renal GGT activities using L-gamma-glutamyl-p-nitroanilide as the substrate. The apparent Km values of pulmonary and renal GGTs were not significantly different. The pulmonary apparent maximum velocity was several orders of magnitude lower than that of the kidney. Inhibition studies, employing L-serine in the presence of 20 microM borate, revealed similar apparent Ki values. Pulmonary GGT behaves similar to renal GGT in respect to its affinity for substrates and inhibitors but has significantly less activity on a gram protein basis.