Evidence for an associative mechanism in the phosphoryl transfer step catalyzed by rabbit muscle creatine kinase.
J Biol Chem
; 255(9): 3944-51, 1980 May 10.
Article
em En
| MEDLINE
| ID: mdl-7372661
ABSTRACT
Creatine kinase does not catalyze the scrambling of 18O in adenosine 5'-[alpha beta-18O, beta-18O2]triphosphate in the absence of creatine, in the presence of L-arginine or taurocyamine (competitive inhibitors of creatine), or in the presence of poor substrates where single turnover experiments were performed. In order to support this prima facie evidence for an associative mechanism of phosphoryl transfer, an investigation was undertaken of 1-carboxymethyl-2-aminoimidazole, a new substrate analogue of creatine. This analogue has a binding constant for rabbit muscle creatine kinase similar to creatine and 1-carboxymethyl-2-iminoimidazolidine, but the initial rate of phoshorylation by MgATP in the presence of creatine kinase is almost 5 orders of magnitude slower. The phosphorylation product, assigned the structure 1-carboxymethyl-2-imino-3-phospho-4-imidazoline is also a poor substrate for the phosphorylation of MgADP by creatine kinase. These observations can be accounted for by an associative SN2(P) mechanism of phosphoryl transfer and by a microenvironment of the enzyme-bound creatine (or creatine analogue) which lowers the pKa of the guanidino group by several pH units compared with that in aqueous solution.
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Base de dados:
MEDLINE
Assunto principal:
Creatina Quinase
/
Músculos
Tipo de estudo:
Risk_factors_studies
Limite:
Animals
Idioma:
En
Ano de publicação:
1980
Tipo de documento:
Article