Kinetics of the conversion of leukotriene C by gamma-glutamyl transpeptidase

γ-Glutamyl transpeptidase (EC 2.3.2.2) converts leukotriene C to leukotriene D by removal of a glutamyl residue. The Michaelis constant for leukotriene C₄ hydrolysis was found to be 5.6 μM. Under the same conditions the K_m value for hydrolysis of reduced glutathione was 5.7 μM. This suggests that leukotriene C₄ and glutathione may be competing substrates for γ-glutamyl transpeptidase under physiological conditions. The apparent K_I for inhibition of leukotriene C₄ hydrolysis by equimolar amounts of L-serine and sodium borate was 0.8 mM.