[Regulation of the activity of brain cytoplasmic creatine kinase by pyridine nucleotides].

Effect of oxidized and reduced forms of pyridine nucleotides on activity of creatine kinase BB was studied in rat brain. NAD did not affect the enzymatic activity at concentrations of 1.0-4.0 mM, while in presence of NADH activity of creatine kinase BB was gradually decreased as the coenzyme concentration increased. The plot of 1/V against 1/S at various NADH concentrations produced a series of lines intersecting at one point (-1/Km), thus indicating the noncompetitive type of brain cytoplasmic creatine kinase inhibition by reduced pyridine nucleotides. Apparent Ki value for NADH was about 1.5 mM which was lower than the known parameter for cytoplasmic creatine kinase isozymes from skeletal and heart muscles. Dependence of brain creatine kinase BB on the rate of pyridine nucleotide reduction suggested a possible mechanism for the enzyme regulation under hypoxic conditions.