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Endogenous Action of Cysteine Endopeptidase and Three Carboxypeptidases on Triticale Prolamins

¹Department of Biochemistry, Warsaw University of Life Sciences–SGGW, Nowoursynowska 159, 02-776 Warsaw, Poland. ²Corresponding author. E-mail: adam_drzymala@sggw.pl

Quantitative and qualitative changes occurring in the prolamin fraction in the starchy endosperm of triticale grains were analyzed by SDS-PAGE on consecutive days of germination. The most intensive hydrolysis of prolamins was observed after the second day of the process. The high molecular weight fractions of prolamins were degraded with the highest rate. Endopeptidase EP8 was capable of hydrolyzing all fractions of prolamins isolated from dry triticale grains, but the high molecular weight fractions were the most rapidly degraded by the enzyme. Carboxypeptidases I, II, and III isolated from triticale grains hydrolyzed prolamins proteolytically modified by endopeptidase EP8, whereas intact prolamins were degraded slightly. Differences in the activity of the studied carboxypeptidases against crude prolamins indicate that carboxypeptidase II may be involved in the initiation of the hydrolysis process and, together with carboxypeptidases I and III, participates in the later stages of degradation of prolamins to amino acids. Experiments with exogenous GA₃ demonstrated that the synthesis of EP8 is induced by this hormone and takes place in the aleurone layer. Mass spectrometry analysis showed the enzyme to be a homologue of barley endopeptidase EP-A. Both enzymes belong to the cysteine class endopeptidases.