Biochemistry of frog ribonucleases.

Frogs have unique pyrimidine base-specific RNases, with structures similar to those of turtle, iguana and chicken RNases. Among the four frog RNases discussed here, three from Rana pipiens, R. catesbeiana and R. japonica oocyte cells show antitumour activity, and the latter two show lectin activity towards sialic acid-rich glycoproteins. In this review, (i) we compare their unique primary structures with respect to the locations of their disulphide bridges, three-dimensional structure, base specificity and heat stability as compared with RNase A, and (ii) we summarize current knowledge about the mode of action of lectin and the antitumour activities of the three frog RNases.