[Affinity modification of rabbit skeletal muscle creatine kinase by a fluorescent analog of ATP: gamma-(azidoanalide)-1, N6-ethenoadenosine triphosphate].

A modification of active centers of creatine kinase was performed by fluorescent analog of ATP: gamma-(p-azidoanilidate)-1, N6-etheno ATP. The affinity of the analog to the enzyme and the enzyme protection against modification by substrates were investigated. The stoichiometry of the label binding to the enzyme is 2:1. The results obtained suggest that one subunit of the enzyme is modified more rapidly than the other, the modification rate difference being insignificant. The covalent binding of the analog to the enzyme results in a 4-5 fold increase of fluorescence intensity of the label, probably due to the analog conformational changes of specific interaction with the enzyme. The label bound enhances the fluorescence upon addition of the substrates. The dissociation constant of the enzyme ADP complex calculated from the titration curve is practically equal to the value estimated from experimental data on the use of the fluorescent probe 2-toluidinonaphthalene-6-sulfonate. The possibilities of application of gamma-(p-azidoanilidate)-1,N6-etheno ATP for investigation of functional and structural characteristics of the enzyme are discussed.