Proteinase activities in quiescent and germinating seeds of xHaynaldoticum sardoum

Breakdown of gliadin during germination of xHaynaldoticum sardoum Meletti et Onnis seeds is correlated with the appearance in the endosperms of a proteinase activity, which is absent in the quiescent seed. This activity is optimal at pH 4 and has a maximum stability at pH 4–5. Gel filtration of proteinase activity extracted from quiescent seeds indicates a molecular weight of 60–100 kDa. The proteinase can hydrolyze hemoglobin but not gliadin and is inhibited by pepstatin A and, to a lower extent, by p -chloromercuribenzoic acid (p-CMB). Gel filtrations of crude extracts from germinating seeds reveal two peaks (molecular weight 66 and 21 kDa) of activity against hemoglobin and a shoulder and a peak (molecular weight 21 kDa) of activity on gliadin. The first peak of activity against hemoglobin is inhibited by pepstatin A and p-CMB; the second one is inhibited by p-CMB and leupeptin. As for the gliadin-eluted activity the shoulder is mainly inhibited by pepstatin A and p-CMB, whereas the peak is inhibited by p-CMB and leupeptin. Estimations of the ratios of total nitrogen to α-amino nitrogen, suggest that the enzyme preparations mainly contain proteinases. It is concluded that the proteinases present in the quiescent seeds of xH. sardoum , in particular aspartic proteinases (EC 3.4.23), could play a role as initiator endoproteases or participate in the digestion of modified proteins during the mobilization of reserve proteins. The cysteine proteinases (EC 3.4.22) appearing during the germination seem to account for the hydrolysis of the most abundant class of protein reserves, the prolamins.