title: Comparison of the rat microsomal Mg-ATPase of various tissues.
abstract: The microsomal Mg-ATPase from various rat tissues was compared. After fractionating the microsomal vesicles by sucrose gradient centrifugation, the highest specific activity of the Mg-ATPase was found in the low-density vesicles which contained plasma membrane. A large fraction (25-90%) of the microsomal Ca-independent Mg-ATPase found in each tissue had the following properties: (1) the Km for ATP was 0.2 mM; (2) the rate of ATP hydrolysis by the Mg-ATPase was nonlinear due to an ATP-stimulated inactivation of the enzyme; (3) wheat germ agglutinin, concanavalin A, glutaraldehyde, and antiserum prevented inactivation induced by ATP or AdoPP[NH]P; (4) detergents at relatively low detergent:protein ratios increased the rate of inactivation with little change in the initial rate of ATP hydrolysis; (5) the Mg-ATPase was inactivated by irradiation in the presence of 8-azido ATP. (6) in addition to ATP, the Mg-ATPase was able to hydrolyze CTP, GTP, UTP, ITP, and GTP but was unable to hydrolyze any of the 10 nonnucleotide phosphocompounds which were tested; (7) the bivalent cation requirement of the Mg-ATPase could be provided by Mg2+, Ca2+, Mn2+, Zn2+, or Co2+ but the enzyme was inactive in the presence of Cu2+, Sr2+, Ba2+, or Be2+; (8) the Mg-ATPase activity was not altered by ionophores or inhibitors of the Na,K-ATPase, the Ca,Mg-ATPase or the mitochondrial F1ATPase. These data suggest that a major portion of the microsomal, basal Mg-ATPase activity is due to one unique enzyme found in most if not all tissues.
mesh_terms: D000273:Adipose Tissue / Q000201:enzymology; D000818:Animals; D001921:Brain / Q000201:enzymology; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002499:Centrifugation, Density Gradient; D007668:Kidney / Q000201:enzymology; D008168:Lung / Q000201:enzymology; D008297:Male; D008670:Metals / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D009132:Muscles / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D013154:Spleen / Q000201:enzymology
chemical_list: D008670:Metals; D017301:Ca(2+) Mg(2+)-ATPase