title: Age-related and phenylhydrazine-induced activation of the membrane-associated cathepsin E in human erythrocytes.
abstract: We examined the effects of cell aging and phenylhydrazine-induced oxidant damage on erythrocyte cathepsin E, which is present as a latent, membrane-associated enzyme in normal human erythrocytes. When young erythrocytes isolated from human mature erythrocytes by Percoll density gradient centrifugation were aged in vitro, the membrane-associated cathepsin E was progressively released from the membrane as an active enzyme. During the cell aging up to 100 h, about 40% of the membrane-associated enzyme was activated and solubilized. When phenylhydrazine was incubated with the erythrocytes, it also caused the activation and solubilization of cathepsin E in a dose-dependent and time-dependent manner. Exposure of erythrocytes to 2.5 mM phenylhydrazine for up to 2 h led to about 40% activation of the membrane-associated enzyme. Both aging and phenylhydrazine-treatment were accompanied with an increase in the association of the cytosolic proteins, primarily hemoglobin, with the membrane, which occurred prior to the release of cathepsin E from the membrane. A similar activation for the membrane-associated enzyme was observed with in vitro-aged hemoglobin-free membrane ghosts. Thus, the primary mechanism for activation of cathepsin E in the intact cells seems to be through lesion of the membrane framework that results from increased binding of hemoglobin to the membrane. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting employing polyclonal IgG antibodies for human spectrin and band 3 revealed that breakdown of the membrane proteins was enhanced in both aged and phenylhydrazine-treated cells. The relation between the cathepsin E activation and the membrane protein breakdown is discussed.
authors.affiliation: Department of Pharmacology, Nagasaki University School of Dentistry.
authors.forename: K
authors.initials: K
authors.lastname: Yamamoto
authors.forename: M
authors.initials: M
authors.lastname: Yamada
authors.forename: Y
authors.initials: Y
authors.lastname: Kato
mesh_terms: D020059:Cathepsin E; D002403:Cathepsins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004905:Erythrocyte Aging; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000201:enzymology*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D010659:Phenylhydrazines / Q000494:pharmacology*
chemical_list: D006454:Hemoglobins; D010659:Phenylhydrazines; D002403:Cathepsins; D020059:Cathepsin E