2- , ricin modification

Endo, Y., Mitsui, K., Motizuki, M., and Tsurugi, K. (1987) The mechanism of action of ricin and related toxic lectins on eukaryotic ribosomes. The site and the characteristics of the modification in 28S ribosomal RNA caused by the toxins. J. Biol. Chem. 262, 5908-5912. 

Another modification to the ricin precursor which occurs during or immediately after synthesis is disulphide bond formation [124]. In mature ricin, the B chain contains four intrachain disulphide bonds and it is joined to the A chain by a single interchain bond. These disulphide bonds are formed enzymically by ER protein disulphide isomerase [134, 135] which introduces five intrachain disulphide bonds into nascent proricin, the bond destined to become the interchain disulphide bond joining the A and B chains of mature ricin being formed between cysteine residues present in the A- and B-chain sequences in the proricin. 

Dual analyses of ricin proteins are performed with MALDI-TOF-MS and LC-MS methods. MALDI-TOF-MS analysis is only able to determine an approximate molecular weight (MW) due to posttranslational modifications that cause ricin to be heavily glycosylated. Thus, LC-MS/MS is employed in concert with MALDI-TOF-MS analyses to identify peptides for accurate protein sequencing from a protein digest [80, 82-83]. Typical detection limits for the MALDI-TOF-MS analysis are between 50 ng/mL and 4 pg/mL. The proteomic... 

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