... argininesubstitutionsEach of the RTA variants described above were reassoci-ated with RTB and the cytotoxicity of each of the resultantricin variants was compared to wild-type ricin. RicinR213A and ricin R21 3D ... fungi and bacteria [1]. Ricinconsists of a catalytic A chain (RTA) joined by a singledisulphide bond to a lectin B chain (RTB) that facilitatesboth cell surface binding and entry of the catalyticallyactive ... Symbols indicate the mean of four replicate samples,error bars represent the SD. (A) ricin, d, ricin R213A, j;andricinR21 3D, m.(B)ricin ,d; ricin R258A, j, and ricin R25 8D, m; (C) ricin, d; ricin R48A,...