摘要：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 A1-insensitive Mg2+-ATPase [ATPase I] and NEM- and bafilomycin A1-insensitive (Ca2+-MG2+)-ATPase [ATPase II] [Hayashi H., et al. Chem. Pharm. Bull., 37, 2783-2786 (1992)]. Sobcellular fractionation showed the presence of similar activity of (Ca2+-Mg2+)-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 (Ca2+-Mg2+)-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) Km values for ATP being 21-27 μM (at pH 4.5) and 18-14 μM (at pH 7.0)(in the presence of CaCl2), (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.
