RCA60: Purification and Characterization of Ricin D Isoforms from Ricinus sanguineus

Ricin is one of the well known potent plant toxins extracted from Ricinus communis (Rc). It is documented that ricin can exist in the same plant in different isoforms depending on the bean’s type and the plant variety from which it is purified. Ricinus sanguineus (Rs) is one variety of Ricinus plant grown in France. It was found that ricin D from Rs has different isoforms (R11, R12 and R2). They were found to have the same molecular masses in reduced and non-reduced conditions. Ricin D isoforms from Rs were found to have pI values from 7.0 up to 9.6. Ricin D isoform R12 was found 100 times more toxic than the isoforms R11 and R2.The phospholipase activity of the three ricin D isoforms was tested on 1,2-diplamitoyl-sn-glycero-3-phosphorylcholine. Ricin D isoform R12 showed a specific activity of 4 nmol/h/mg protein compared with 2.5 nmollh/mg protein for R11 and R2. It is hypothesized that this higher phospholipase activity may be related to the increased cytotoxicity of ricin R12 isoform and, in part, accounts for the low cytotoxicity of R11 and R2.