title: Evidence for proximal cysteine and lysine residues present at the nucleotide domain of rabbit muscle creatine kinase.
abstract: Inactivation of rabbit muscle creatine kinase by o-phthalaldehyde was investigated. The loss of enzyme activity was concomitant with the increase in fluorescence intensity at 410 nm. The modified enzyme showed a characteristic absorption peak at 336 nm. These evidences suggested that the mechanisms of inhibition of creatine kinase by o-phthalaldehyde involves binding of the thiol and the epsilon-amino group of enzyme leading to the formation of isoindole derivative. None of the substrates, except Mg-ATP, provided protection against o-phthalaldehyde inhibition. This was corroborated by fluorescence studies. Double inhibition experiments showed that p-chloromercuricphenyl sulphonic acid, a thiol-specific reagent, binds to the same cysteine which is also involved in the o-phthalaldehyde reaction. Stoichiometric results indicated that 2 mol of o-phthalaldehyde were incorporated per mole of enzyme molecule upon complete inactivation. Denaturation of creatine kinase by urea or heat treatment prior to o-phthalaldehyde addition resulted in the decrease of fluorescence intensity indicating that native conformation of the enzyme is essential for isoindole derivative formation.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Kanpur.
authors.forename: S
authors.initials: S
authors.lastname: Sheikh
authors.forename: K
authors.initials: K
authors.lastname: Mukunda
authors.forename: S S
authors.initials: SS
authors.lastname: Katiyar
mesh_terms: D000818:Animals; D003402:Creatine Kinase / Q000737:chemistry / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism*; D009132:Muscles / Q000201:enzymology*; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D013379:Substrate Specificity; D009764:o-Phthalaldehyde / Q000378:metabolism
chemical_list: D009764:o-Phthalaldehyde; D003402:Creatine Kinase; D008239:Lysine; D003545:Cysteine