KINETICS OF SLOW REVERSIBLE INHIBITION OF HUMAN MUSCLE CREATINE-KINASE BY PLANAR ANIONS

The toxicity of NO3- and NO2- to mammals has been widely publicized. H owever, the kinetic mechanism of inhibition of human muscle creatine k inase by NO3- and NO2- has not been explored. The kinetic theory of th e substrate reaction during the modification of enzyme activity previo usly described by Tsou (Adv. Enzymol. Related Areas Mol. Biol. 1988, 6 1, 381-436) has been applied to a study of the kinetics of slow revers ible inhibition of human muscle creatine kinase by planar anions (NO3- and NO2-). The kinetic equation of the substrate reaction was derived from theoretical analysis and experimental data, then simplified. The microscopic rate constants for the reaction of the inhibitors with th e enzyme were obtained from the simplified equation for the substrate reaction in the presence of the inhibitors. The results show that the apparent forward rate constant a is dependent on ATP concentration, in dicating competition between the inhibitor (NO3- or NO2-) and ATP, The results also suggest that binding of creatine-MgADP and the anion wit h the enzyme is very tight, since their binding constants are much hig her than those for normal substrates.