ABSTRACT
Correlation of the structure of ricin A chain with its catalytic activity will aid in the understanding of the mechanism by which it inactivates protein synthesis. The use of ricin A chain as a component of immunotoxins in the treatment of a number of human diseases may present new problems, including immuogenicity, toxicity, and localization to the desired target. Results from trinitrophenylation of whole ricin D suggests that free amino groups exposed on the surface of the whole toxin may be involved in the enzymatic activity of the A chain. Modification of arginine residues in isolated ricin A chain by either phenylglyoxal or 1,2-cyclohexanedione inactivates its inhibitor activity in a cell-free protein synthesis system. When considering the effect of amino acid substitutions or mutations on the catalytic activity of ricin A chain, the background within which the mutations are made must be considered.
