Multiple forms of glycylprolyl dipeptidyl-aminopeptidase (GP-DAP) in human serum were separated by electrophoresis on cellulose acetate and the activities were directly measured fluorometrically on the strip using 7-glycylproline-4methylcoumarinamide as substrate. Human sera from patients with hepatitis had four peaks at the 00, (peak I), fast 002 (peak II), 0:2 (peak III), and ,3 (peak IV) regions. Normal sera showed mainly peak III. The sera from patients with hepatitis showed increased total enzyme activity and elevation in the two new peaks, peak I and peak II. When sera from patients with hepatitis were heated at 60°C for 30 min, the peaks I, II and III were decreased by about 25 %, and peak IV completely disappeared, indicating a different heat stability for each enzyme form. When human sera from patients with hepatitis were treated with neuraminidase, all the peaks shifted to the cathode except for peak IV, and the ratio between the three peaks changed greatly. These results suggest that the multiple forms of human serum GP-DAP may be due to different contents of sialic acid.

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