Abstract
Ricin D, a toxic protein from castor bean, was found to contain 6 moles of glucosamine and 17 moles of mannose per mole of protein.
Isolation of two constituent polypeptide chains, namely Ala-chain and Ile-chain, and subsequent proteolytic digestions with Nagarse and Pronase revealed two glycopeptides (Asp1, Thr1 Gly1, glucosamine2 mannose6 and Asp1 Thr1 Glu1 Pro1 glucosaminez mannose7) from Alachain and one (Asp1 Ile1 Phe1 glucosamine2 mannose4) from Ile-chain. The total carbohydrate content of these glycopeptides accounts for all that of the whole protein. It is therefore that carbohydrate moieties are covalently linked to the polypeptide chains in three sites to form this glycoprotein.
