... on ice for 30 min, andcentrifuged at 16 000 g for 30 min. The final supernatantwas assayed for protein concentration and frozen at )80 °C,or processed immediately. All steps were performed ... quaternary isoforms, isoenzymes, monomeric forms;assay for selective cytotoxicity of the enzyme. Methods Enzymol.341, 248–263.13. Kunitz, M. (1946) A spectrophotometric method for the meas-urement ... illustrated in Table 1, were prepared followingestablished procedures [12] for the derivatization of Cys31and Cys32, the cysteine residues that form the intersub-unit disulfides of BS-RNase. Briefly,...