Properties of Some Heart Sarcolemmal-bound Enzymes*
- 1 September 1974
- journal article
- research article
- Published by Oxford University Press (OUP) in The Journal of Biochemistry
- Vol. 76 (3) , 603-609
- https://doi.org/10.1093/oxfordjournals.jbchem.a130604
Abstract
Both Ca2+ and Mg2+ stimulated ATP hydrolysis by the dog heart sarcolemmal fraction. The mean Km values were 0.90 and 0.95 mM and the mean Vmax values were 17.2 and 16.0 μmoles P1/mg per hr for the membrane Ca2+ ATPase [EC 3.6 1.3] and Mg2+ ATPase respectively. Other divalent cations such as Mn2+, Co2+, and Ni2+ were also found to stimulate ATP hydrolysis in this fraction. Excess of ATP was inhibitory to the ATP hydrolysis due to various divalent cations. Ni2+, Co2+, Mg2+, and Mn2+ were shown to depress the ATP hydrolysis due to Ca2+. The Ca2+ ATPase activity in the heart membranes was also inhibited by Na+ whereas K+ had no effect. The adenylate cyclase activity of the heart membranes was increased by about 35% and 4 fold by epinephrine and NaF respectively. These agents increased Vmax (286 pmoles cyclic AMP/mg per min) without any changes in the Km value (0.08 mM) for ATP. The activation of adenylate cyclase [EC 4.6.1.1] due to epinephrine was blocked by a well known β-adrenergic blocking agent, propranolol.Keywords
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