PURIFICATION AND SOME PROPERTIES OF RIBONUCLEASE FROM XENOPUS-LAEVIS EGGS

A 122 kDa RNase from eggs of Xenopus laevis was purified by sequential chromatography on Sephadex G-75, DEAE-cellulose, heparin-Sepharose an d TSK gel G3000SW columns, and gave a single 60 kDa band on SDS-polyac rylamide gel electrophoresis under reducing and nonreducing conditions . The RNase composed of two 60 kDa subunits is able to recognize pyrim idine bases specifically. The pH optimum of the RNase was 7.5 in Tris- HCl buffer. The enzyme activity was abolished by treatment at 80-degre es-C for 5 min and pH 2 or 12 for 1 h. Since egg lectins with RNase ac tivity obtained from Rana catesbeiana and R. japonica and bovine pancr eatic RNase A show about 30% protein homology and these three proteins are 12-14 kDa heat-stable RNases, [K. Titani, K. Takio, M. Kuwada, K. Nitta, F. Sakakibara, H. Kawauchi, G. Takayanagi and S. Hakomori, Bio chemistry, 26, 2189 (1987); Y. Kamiya, F. Oyama, R. Oyama, F. Sakakiba ra, K. Nitta, H. Kawauchi, Y. Takayanagi and K. Titani, J. Biochem. (T okyo), 108, 139 (1990)], the data suggest that the X. laevis egg RNase is a unique protein compared with RNases from not only amphibians, bu t also mammals.