In Vitro Stability and Inactivation of Peptide Hydrolases Extracted from Phaseolus vulgaris L
Feller, Urs
In: Plant and Cell Physiology, 1981, vol. 22, no. 6, p. 1095-1104
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- Endopeptidase activity against azocasein had a higher temperature optimum (50°C) in leaf extracts than in cotyledon extracts (37°C). The temperature optima for aminopeptidase (46°C) and for carboxypeptidase (53°C) were similar in leaf and cotyledon extracts. The endopeptidase activity showed an excellent stability in crude extracts from leaves even at 37°C, while the endopeptidase in cotyledon extracts was less stable. Carboxypeptidase was very stable in both leaf and cotyledon extracts. Aminopeptidase was the least stable of the enzymes investigated and its inactivation rate depended on the source of the extract. A moderate stability was observed in extracts of leaves or of ungerminated seeds, but this enzyme was rapidly inactivated in cotyledon extracts at pH 5.4. At pH 7.5 aminopeptidase remained active longer than at pH 5.4. From experiments with mixed extracts it could be concluded that in cotyledons an aminopeptidase inactivating factor was formed during germination. This factor was heat sensitive, excluded by Sephadex G-25, precipitated by 75% ammonium sulfate and inhibited by tosyl-L-lysine chloromethyl ketone. These data suggest that the factor is a protein and considering the similar properties it appears possible that it is the endopeptidase formed during germination