IN-VITRO PROTEOLYSIS OF NARBONIN

Narbonin, the 2 S globulin of Vicia narbonensis seeds is very slowly h ydrolysed by 5 of the 7 exogenous proteinases tested and is remarkably resistant to the hydrolysis by the seed proteinase A the key enzyme o f storage proteins degradation. It is rapidly hydrolysed only by pepsi n at low pH where narbonin is presumably denatured. A profound but muc h slower cleavage was also observed when hydrolysis by trypsin was per formed. The one-by-one type of proteolysis takes place under the actio n of all proreinases studied. In the case of trypsin hydrolysis format ion of intermediate high molecular mass fragments (zipper-type proteol ysis) occurs in parallel. The sites of cleavage leading to the formati on of these fragments are located in hydrophilic and exposed parts of the narbonin molecule. The slow rate of narbonin hydrolysis by several exogenous proteinases and, especially, the insensitivity to the actio n of proteinase A provides an additional argument against the classifi cation of narbonin to the storage proteins.