MODIFICATION OF DNA TOPOISOMERASE-I ENZYMATIC-ACTIVITY WITH PHOSPHOTYROSYL PROTEIN PHOSPHATASE AND ALKALINE-PHOSPHATASE FROM THE HEPATOPANCREAS OF THE SHRIMP PENAEUS-JAPONICUS (CRUSTACEA, DECAPODA)

DNA topoisomerase I was partially purified from the hepatopancreas of the shrimp Penaeus japonicus. nle specific activity of the final prepa ration was 7,000,000 units/mg of protein with SV40 viral DNA as substr ate. SDD-polyacrylamide gel electrophoresis of the final preparation y ielded two major bands of proteins with M(r) 70,000 and M(r) 67,000, a s well as less intense bands of proteins with M(r) 64,000 and M(r) 56, 000. Incubation of the partially purified enzyme fraction with rabbit antiserum against human DNA topoisomerase I, allowed all these protein s except that of M(r) 56,000, to be positively reacted. Treatment of t he partially purified DNA topoisomerase I with tyrosine kinase p43(v-a bl) resulted in phosphorylation of only the two major subunits. Phosph orylation by tyrosine kinase p43(v-abl) or dephosphorylation by phosph otyrosyl protein phosphatase resulted in a decrease of the enzymatic a ctivity. The treatment with shrimp alkaline phosphatase abolished the enzymatic activity of the purified DNA topoisomerase I in a dose-depen dent manner. Thus, the DNA topoisomerase I was apparently isolated fro m the hepatopancreas of the shrimp P. japonicus in a phosphorylated fo rm, and this phosphorylation was essential for expression of enzymatic activity in vitro. The activity of DNA topoisomerase I is inhibited b y ZnCl2, CuCl2 and Pb(NH3)(3) at millimolar concentrations, but less i nhibition was observed with CaCl2.