The distribution of the enzymes in resting cereals II. The distribution of the proteolytic enzymes in wheat, rye, and barley

Selective proteolysis of the wheat Em polypeptide. Identification of an endopeptidase activity in germinating wheat embryos

The 'Em' polypeptide is the most abundant cytosolic polypeptide in mature wheat embryos. It is selectively and completely degraded within the first 24 h of germination. Extracts from germinated embryos contain endopeptidase activities which degrade the Em polypeptide. These are separable into a major and minor component by ion-exchange chromatography and the use of inhibitors shows the major component to be a cysteine proteinase. This activity shows a strong preference for the Em polypeptide as a substrate, being inactive against polypeptides which are not developmentally regulated and showing only low activity towards developmentally related, but otherwise nonhomologous 'dehydrin' polypeptides.

Localization and activity of various peptidases in germinating barley

Germinating barley grains contain at least eight different peptidases: three carboxypeptidase (pH optima 4.8, 5.2, and 5.7), three aminopeptidases which act on aminoacyl-β-naphthylamides (pH opitima in the hydrolysis of di- and tripeptides at pH 5.8-6.5), and two peptidases which hydrolyse Ala-Gly and Leu-Tyr optimally at pH 7.8 and 8.6 respectively. We have determined the activities of these enzymes in the different tissues of non-germinated grains and followed the changes in the activities during a 5-day germination at 16°C.The aleurone layers contain high activities of all three groups of peptidases; there are no changes in the activities of the five aminopeptidases on germination, while the carboxypeptidases exhibit a small increase of activity. The starchy endosperms contain high carboxypeptidase activities, which increase during germination, but are totally devoid of the five aminopeptidases.All the peptidases exhibit high activities in the scutella; the carboxypeptidases and the enzymes acting on Ala-Gly and Leu-Tyr increase in activity during germination, while the "naphthylamidase" activities remain constant.The three peptidase groups occur in the seedling as well, but compared to the other tissues the carboxypeptidase activities are very small and the "naphthylamidase" activities are very high. The last-named enzymes seem to be characteristic for growing tissues.The starchy endosperm contains about two thirds of the total reserve proteins of the grain. Its internal pH during germination is 5.0-5.2, a value at which all the carboxypeptidases are highly active. As these enzymes are present in high concentrations in this tissue, it is probable that they have a central role in the mobilization of the reserve proteins during germination. The high peptidase activities of the scutellum, on the other hand, suggest that some of the hydrolysis products are absorbed as peptides and these are further hydrolysed to amino acids in this tissue.