Chemical conjugation of Gly-Pro-Arg-Pro. Tetrapeptide to low molecular weight urokinase.

Two low molecular weight urokinase derivatives were obtained by covalent coupling of a synthetic Gly-Pro-Arg-Pro tetrapeptide to peptide A of low molecular weight urokinase and exchanging the native peptide A of low molecular weight urokinase with Gly-Pro-Arg-Pro-peptide A to obtain derivative I or direct conjugation of Gly-Pro-Arg-Pro tetrapeptide to low molecular weight urokinase to obtain derivative II. In caseinolytic assay, fibrin can stimulate the two derivatives to activate plasminogen. But the two derivatives showed different kinetic behaviors. The derivative I displayed immediate onset of lysis and derivative II displayed a lag phase.