BIOCHEMISTRY OF FROG RIBONUCLEASES

Frogs have unique pyrimidine base-specific RNases, with structures sim ilar to those of turtle, iguana and chicken RNases. Among the four fro g RNases discussed here, three from Rana pipiens, R. catesbeiana and R . japonica oocyte cells show antitumour activity, and the latter two s how lectin activity towards sialic acid-rich glycoproteins. In this re view, (i) we compare their unique primary structures with respect to t he 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 an d the antitumour activities of the three frog RNases.