Abstract
Assaying conditions of serum γ-glutamyl transpeptidase (γ-GTP, EC. 2. 3. 2. 2.) were studied using L-γ-glutamyl-4-nitroanilide as the substrate on the basis of the conditions recommended by the Scandinavian Society of Clincal Chemistry (S. S. C. C.). The optimum conditions obtained were different from that of the S. S. C. C. as follows; pH (7.6 to 8.1), MgCl2 (10mM→none), and NaCl (none→100mM). The optimum pH was found to be between 7.9 and 8.3 (mean 8.1, at 37°) ; not only with Tris buffer but also with many other buffers. The concentrations of buffers used were all optimal at 100mM.
The apparent activation of γ-GTP activity by various inorgnic salts was also studied. The rate of activation with MgCl2 was found to be only slight (about 102%), and those with NaCl and KCI were from 110 to 120%. Thi sactivating effect by manys alts could not be found by utilizing a soluble substrate, L-γ-glutamyl-3-carboxy-4-nitroallilide. This suggests that the activating phenomenon is caused by the alteration of substrate solubility by the salts.
A solution of γ-glutamyl-4-nitroanilide solubilized with HCI was unstable at room temperature, and the degradated products inhibited γ-GTP activity. The inhibition rate was 4 percent per hour at room temperature.
