title: Exploration of the polar microenvironment around the reactive cysteine in rabbit muscle creatine kinase.
abstract: The polar microenvironment around the reactive Cys283 of rabbit muscle creatine kinase was explored using kinetic analysis of substrates reaction in the presence of modifiers. In the present study, three specific sulphydryl reagents, 5,5'-dithiobis(2-nitrobenzoic acid), 6,6'-dithiodinicotinic acid and 2,2'-dithiodipyridine, were applied as modifiers to react with Cys283 of creatine kinase. The inactivation kinetics of creatine kinase by the modifiers was analyzed. The microscopic rate constants for reactions of the modifiers with free enzyme and enzyme-substrate complexes were also determined. The results suggested that the inactivation rate of creatine kinase by 5,5'-dithiobis(2-nitrobenzoic acid) was the fastest, followed by 6,6'-dithiodinicotinic acid and then 2,2'-dithiodipyridine. Interestingly, 5,5'-dithiobis(2-nitrobenzoic acid) and 6,6'-dithiodinicotinic acid functioned as non-complexing modifiers, while 2,2'-dithiodipyridine did a complexing modifier. The results here indicated that the electrophilic group was predominant around Cys283, and that the presence of substrates seemed to have different effects on the inactivation reactions of creatine kinase by the three modifiers. Furthermore, the findings in this study may provide a novel explanation for the low pKa value of Cys283.
authors.affiliation: Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, PR China.
authors.forename: Hua-Wei
authors.initials: HW
authors.lastname: He
authors.forename: Jie
authors.initials: J
authors.lastname: Li
authors.forename: Tong-Jin
authors.initials: TJ
authors.lastname: Zhao
authors.forename: Yong
authors.initials: Y
authors.lastname: Ma
authors.forename: Feng
authors.initials: F
authors.lastname: Shi
authors.forename: Hai-Meng
authors.initials: HM
authors.lastname: Zhou
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D003401:Creatine / Q000494:pharmacology; D003402:Creatine Kinase / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry / Q000494:pharmacology; D004228:Dithionitrobenzoic Acid / Q000737:chemistry / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D015394:Molecular Structure; D009132:Muscles / Q000201:enzymology*; D009539:Nicotinic Acids / Q000737:chemistry / Q000494:pharmacology; D011817:Rabbits; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D004220:Disulfides; D009539:Nicotinic Acids; D013438:Sulfhydryl Compounds; C001102:6,6'-dithiodinicotinic acid; C001105:2,2'-dipyridyl disulfide; D015082:2,2'-Dipyridyl; D000255:Adenosine Triphosphate; D004228:Dithionitrobenzoic Acid; D003402:Creatine Kinase; D003545:Cysteine; D003401:Creatine