title: The [Ca2+ + Mg2+]-dependent adenosine triphosphatase of SV40 transformed WI38 lung fibroblasts.
abstract: The Ca2+-stimulated, Mg2+-dependent ATPase of SV40 transformed WI38 lung fibroblast homogenates exhibits a high affinity for Ca2+ (K0.5 = 0.20 microM) and moderately high affinity for ATP (Km = 28.6 microM) and Mg2+ (K0.5 = 138.5 microM). This activity was NaN3, KCN and oligomycin insensitive but very sensitive to vanadate (I50 = 0.5 microM) suggesting its being neither mitochondrial or microsomal but plasma membrane in origin. Under optimal conditions of protein, hydrogen ion and substrate concentration, 16-19 nmoles phosphate was released per min per mg protein. Hill plot analysis indicated no cooperativity to occur between Ca2+ binding sites. Nucleotides other than ATP and dATP were ineffective as substrates. The trivalent cation, lanthanum (La3+) completely inhibited hydrolysis of ATP at approximately 70 microM (I50 = 25 microM). Calmodulin antagonists trifluoperazine and calmidazolium inhibited ATP hydrolysis in a dose dependent fashion.
authors.affiliation: Brain Research Laboratory of Biochemistry, University of Texas, San Antonio.
authors.forename: J L
authors.initials: JL
authors.lastname: Bermudez
authors.forename: J P
authors.initials: JP
authors.lastname: Chambers
authors.forename: E
authors.initials: E
authors.lastname: Rizopoulos
authors.forename: P
authors.initials: P
authors.lastname: Kumar
authors.forename: J J
authors.initials: JJ
authors.lastname: Valdes
authors.forename: A O
authors.initials: AO
authors.lastname: Martinez
mesh_terms: D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009711:Nucleotides / Q000378:metabolism; D012977:Sodium Nitrite / Q000494:pharmacology; D013379:Substrate Specificity; D014638:Vanadates / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D009711:Nucleotides; D014638:Vanadates; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D012977:Sodium Nitrite; D002118:Calcium