THE ANTITUMOR ACTION OF SEMINAL RIBONUCLEASE AND ITS QUATERNARY CONFORMATIONS

It has been previously shown that the antitumor action of bovine semin al ribonuclease (BS-RNase) is dependent on its dimeric structure. Howe ver, two distinct quaternary structures, each in equilibrium with the other, have been described for the enzyme: one in which the two subuni ts exchange their N-terminal ends, the other with no exchange. Antitum or activity assays, carried out on homogeneous quaternary forms of the enzyme, as well as on dimeric mutants of bovine pancreatic RNase A, r eveal that another structural determinant of the antitumor activity of BS-RNase is the exchange of N-terminal ends between subunits.