Enzymatic properties of two calcium-stimulated ATPases in the neutral and acidic pH regions found in the membrane fraction of human milk

• Published in: Bioscience, biotechnology, and biochemistry Vol. 56; no. 6; pp. 900 - 905
• Main Authors: Kanno, C. (Utsunomiya Univ. (Japan)), Takeda, Y, Cho, J.K
• Format: Journal Article
• Language: English
• Published: Tokyo Taylor & Francis 1992; Japan Society for Bioscience Biotechnology and Agrochemistry; Oxford University Press
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; ADENOSINA TRIFOSFATASA; ADENOSINE TRIPHOSPHATASE; Analytical, structural and metabolic biochemistry; Biological and medical sciences; CALCIO; CALCIUM; Enzymes and enzyme inhibitors; ENZYMIC ACTIVITY; Fundamental and applied biological sciences. Psychology; HUMAN MILK; Hydrolases; LAIT HUMAIN; LECHE HUMANA; MEMBRANA; MEMBRANE; MEMBRANES; Characterization; Substrate; Ca-ATPase; Enzymatic activity; Enzyme; Membrane fraction; Human milk; pH; Kinetics; Inhibition
• ISSN: 0916-8451; 1347-6947
• DOI: 10.1271/bbb.56.900

Two calcium-stimulated ATPases at optimal pH values of 5.0 and 7.0, which are designated as acid and neutral Ca 2+ -ATPase, respectively, were found in the membrane fraction of human milk, and their enzymatic properties were studied. For maximal activity, neutral Ca 2+ -ATPase required 0.45 mM Ca ion, while acid Ca 2+ -ATPase required 207 mM Ca ion. Neutral Ca 2+ -ATPase activity was not enhanced by adding the Mg ion at more than 0.1 mM. Among the nucleotides, neutral Ca 2+ -ATPase showed a higher substrate specificity to GTP, CTP, ITP, and UTP than to ATP, while ATP was the best substrate for acid Ca 2+ -ATPase. Neutral and acid Ca 2+ -ATPases had apparent K m values of 0.361 and 0.192 mM, and V max of 186 and 178 μmol ATP hydrolyzed/mg of protein per min, respectively. Both Ca 2+ -ATPases were potently inhibited by fluoride, lanthanide, vanadate, and p-chloromercuribenzoate, and inactivated by EDTA, EGTA, and CDTA, but were unaffected by N-ethylmaleimide, NaN 3 , ouabain, oxidized glutathione, or oligomycin, and were inactivated by heating at 60°C for 10 min. These enzymes were concentrated in the membrane fraction of the cream and skim milk membrane.