Involvement of arginine residues in inhibition of protein synthesis by ricin A-chain.

Modifications of arginine residues in ricin A-chain with phenylglyoxal (PGO) and 1,2-cyclohexanedione (CHD) caused a marked loss in its inhibitory activity on cell-free protein synthesis. The loss of activity caused by modification with PGO was much faster than the loss of total arginine residues. More than 90% activity was lost with PGO modification of about three arginine residues. Regeneration of arginine residues from the CHD-modified residues resulted in complete recovery of the activity. These results strongly suggest the involvement of definite arginine residue(s) in A-chain activity. Analysis of the peptides, produced by peptic digestion of the [14C]PGO-modified A-chain, showed that some of the six arginine residues in the N-terminal region of A-chain react with PGO faster than other arginine residues.