MAJOR PROTEINASE HYDROLYZING GLIADIN DURING WHEAT GERMINATION

A proteinase, representing the bulk of the enzyme activity for the hyd rolysis of gliadin, was extracted from endosperms isolated from germin ated seeds (four days) and was purified by ion-exchange chromatography and preparative isoelectric focusing. The optimal pH for gliadin hydr olysis was 4.25. The M(r), determined by sodium dodecyl sulphate-polya crylamide gel electrophoresis, was 30 000; the isoelectric point was 4 .5. The enzyme activity was totally inhibited by E-64 and cystatin, wh ile inhibitors of other classes of proteinases were barely effective o r ineffective. The activity was stimulated by sulphhydryl compounds. T he proteinase hydrolysed to small peptides the gliadins from durum and soft wheat seeds. Other protein substrates were weakly degraded or no t degraded. The proteinase appears to belong to the cysteine class and to play a key role in the initial mobilization of the main reserve pr otein in the starchy endosperm. Copyright (C) 1996 Elsevier Science Lt d