A Comparative Study of (Ca^<2+>-Mg^<2+>)-ATPase on the Lysosomal Membrane and ecto-ATPase on the Plasma Membrane from Rat Liver

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We showed that ratl liver lysosomes possess at least two types of ATPase besides H^+-translocating ATPase (H^+-ATPase); namely, N-ethylmaleimide (NEM)-sensitive and bafilomycin A_1-insensitive Mg^<2+>-ATPase [ATPase I] and NEM- and bafilomycin A_1-insensitive (Ca^<2+>-MG^<2+>)-ATPase [ATPase II] [Hayashi H., et al. Chem. Pharm. Bull., 37,2783-2786 (1992)]. Sobcellular fractionation showed the presence of similar activity of (Ca^<2+>-Mg^<2+>)-ATPase not only in the Golgi but also in the plasma membrane fractions, of which plasma membrane had the highest activity, most probably due to the ecto-ATPase. In this study, we partially purified the (Ca^<2+>-Mg^<2+>)-ATPases from both lysosomal and plasma membranes and compared their properties. Both enzymes had quite similar characteristics including : (1) broad pH-activity profiles with two pH optima at 4.5 and 7.0,(2) K_m values for ATP being 21-27 μM (at pH 4.5) and 18-14 μM (at pH 7.0)(in the presence of CaCl_2), (3) hydrolysis of both nucleoside triphosphates and diphosphate (ADP), (4) inhibition only by vanadate and 4,4'-diisothiocyanatostilbene 2,2'-disulfonic acid (DIDS) at pH 4.0 (but not at pH 7.0), (5) acidic pI values that were shifted by neuraminidase digestion, and (6) a positive reaction against an antibody to the N-terminal peptide of ecto-ATPase.
公益社団法人日本薬学会の論文
1996-10-15