Major proteinases hydrolyzing gliadin during wheat germination

A proteinase, representing the bulk of the enzyme activity for the hydrolysis of gliadin, was extracted from endosperms isolated from germinated seeds (four days) and was purified by ion-exchange chromatography and preparative isoelectric focusing. The optimal pH for gliadin hydrolysis was 4.25. The M r, determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis, was 30 000; the isoelectric point was 4.5. The enzyme activity was totally inhibited by E-64 and cystatin, while inhibitors of other classes of proteinases were barely effective or ineffective. The activity was stimulated by sulphhydryl compounds. The proteinase hydrolysed to small peptides the gliadins from durum and soft wheat seeds. Other protein substrates were weakly degraded or not degraded. The proteinase appears to belong to the cysteine class and to play a key role in the initial mobilization of the main reserve protein in the starchy endosperm