Plant Physiol. Illumina
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Plant Physiology 70:1367-1372 (1982)
© 1982 American Society of Plant Biologists

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Articles

Characteristics and Activity Changes of Proteolytic Enzymes in Apple Leaves during Autumnal Senescence

Seong-Mo Kang, Hiroyuki Matsui1 and John S. Titus

Department of Horticulture, University of Illinois, Urbana, Illinois 61801

At least four different proteinases are present in senescing apple leaves (Malus domestica Borkh. cv. Golden Delicious) as determined by their pH optima, substrate specificity, and their reactivity to proteinase inhibitors. An enzyme active at pH 4.5 to 5.0 appears to be a sulfhydryl-dependent (iodoacetamide and phenylmercuric acetate-sensitive) endoproteinase, and degradation of the large subunit of ribulose bisphosphate carboxylase was observed only with this enzyme. It is tentatively concluded that this endoproteinase is responsible for the breakdown of ribulose bisphosphate carboxylase in vivo. However, the presence of more than one endoproteinase in apple leaves is suggested by the broad range of pH optima of the SH-dependent enzyme. Another enzyme active at pH 6.0 appears to be a carboxypeptidase, and was sensitive to phenylmethylsulfonylfluoride. This enzyme showed a strong hydrolytic activity against carbobenzoxyphenylalanylalanine. A sulfhydryl-dependent aminopeptidase and a second hydroxyl-dependent carboxypeptidase were active at pH 7.5

Total autolytic activity (the sulfhydryl-dependent endoproteinase) as measured by the disappearance of proteins decreased during the period of protein decline. Evidence is presented that the measured proteinase activity can be dependent on assay methods and substrates. While the disappearance of protein measures most of endo-type activity, the ninhydrin assay appears to measure exo-type activity preferentially.

1 On leave from the Department of Horticulture, University of Osaka Prefecture, Sakai, Osaka, Japan.






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ASPB Publications PLANT PHYSIOLOGY® THE PLANT CELL
Copyright © 1982 by the American Society of Plant Biologists