Creatine Kinase of Rat Heart Mitochondria
Abstract
Abstract Intact mitochondria from human, beef, and rat heart, as well as rat brain and rat skeletal and smooth muscle, contain considerable creatine kinase activity; those from rat or rabbit liver, kidney, and testis contain essentially none. In rat heart mitochondria creatine kinase activity is far higher than the activity of adenylate kinase and nucleoside diphosphokinase. The heart mitochondrial creatine kinase is specific for ATP and ADP as phosphate donor and acceptor. The optimum pH is 6.7 in the direction of ATP formation and 8.0 in the direction of phosphocreatine formation. The mitochondrial isoenzyme of creatine kinase is not present in the same compartment as the intermembrane marker enzyme adenylate kinase, but may be released in soluble form by exposure to sodium acetate or sodium phosphate medium at pH 7.4. The phosphorylation of creatine by intact mitochondria takes place outside the atractyloside-sensitive ADP-ATP carrier system of the inner membrane and thus requires external ATP. When creatine in the concentration range known to be present in intact heart is added to rat heart mitochondria neither the initial State 4 or State 3 rate of respiration (succinate) is affected; however, there is a large increase in the State 4 rate following addition of ADP, whose magnitude increases as the creatine concentration is increased. In the presence of physiological concentrations of creatine and ADP rat heart mitochondria respire at a constant high rate equal to 75 to…
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