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Calcium‐stimulated ATPase activity in homogenates of the secretory enamel organ in the rat
Author(s) -
MÖRNSTAD HÅKAN
Publication year - 1978
Publication title -
european journal of oral sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.802
H-Index - 93
eISSN - 1600-0722
pISSN - 0909-8836
DOI - 10.1111/j.1600-0722.1978.tb00601.x
Subject(s) - iodoacetic acid , chemistry , oligomycin , atpase , sodium azide , calcium , atp hydrolysis , hydrolysis , substrate (aquarium) , sodium , biochemistry , incubation , acid phosphatase , phosphatase , enamel paint , enzyme , chromatography , nuclear chemistry , organic chemistry , biology , medicine , dentistry , ecology
— The activity of calcium‐stimulated ATPase (E.C. 3.6.1.3) in homogenates of the secretory enamel organ of rat incisors was studied biochemically. ATP hydrolysis was estimated from the amount of inorganic phosphate liberated. An analysis of the total degradation of ATP was initially performed to ensure that the enzyme assays pertained to the original substrate, ATP, and were not influenced by reaction products formed. Standard incubations were run in trismaleate buffer, pH 8.2, with 3 mM ATP, 3 rnM Ca 2+ and 0.5 mM R8231 at 37°C. The presence of R 8231 was necessary to inhibit nonspecific alkaline phosphatase. The calcium‐stimulated ATPase was completely inhibited when heated at 55–60°C for 5 min. The pH optimum was found to be 8.2. The hydrolysis was substantially dependent on Ca 2+ and was fastest when the ATP:Ca 2+ ratio was 1:1. High substrate concentrations inhibited the hydrolysis. The addition of 1 mM Zn 2+ and Ni 2+ to the incubation medium markedly inhibited the hydrolysis as did, though less strongly, p ‐hydroxymercuribenzoate, oligomycin, EDTA and ruthenium red. l ‐Cysteine, mercaptoethanol, iodoacetic acid and sodium azide were without effect. F. was without effect unless added to a final concentration above 15 mM to media where Ca 2+ had first been allowed to react with ATP.