A NOVEL PHOSPHOLIPASE-C INHIBITOR, S-PLI PRODUCED BY STREPTOMYCES SP STRAIN NO A-6288

S-PLI, an inhibitor of phospholipase C (PLC) produced by Streptomyces sp, strain No. 6288, was purified from the culture filtrate by salting -out with solid ammonium sulfate, column chromatography on CM-cellulos e and gel filtration on Sephadex G-75. The molecular weight of S-PLI w as estimated to be 65,000 by SDS-polyacrylamide gel electrophoresis. T he inhibitor was found to be a glycoprotein with a composition of 609 amino acids and 19 glucose residues having an isoelectric point at 7.8 . S-PLI was stable from pH 3 to 10 at 37 degrees C and up to 40 degree s at pH 6.0. The inhibitory activity showed pH- and temperature-depend ence with a maximum around pH 7.0 at 50 degrees C. S-PLI inhibited pho spholipase C in a competitive manner (K-i value; 9.5 x 10(-6) mM), but did not inhibit S-Hemolysin, phospholipase A(2), phospholipase B, pho spholipase D and phosphatases. S-PLI is the first reported example of a glycoproteinaceous inhibitor of microbial origin which is able to sp ecifically inhibit phospholipase C.