Author/Editor		Goličnik, Marko; Olguin, Luis F; Feng, Guoqiang; Baxter, Nicola J; Waltho, Jonathan P; Williams, Nicholas H; Hollfelder, Florian
Title		Kinetic analysis of beta-phosphoglucomutase and its inhibition by magnesium fluoride
Type		članek
Source		J Am Chem Soc
Vol. and No.		Letnik 131, št. 4
Publication year		2009
Volume		str. 1575-88
Language		eng
Abstract		The isomerization of beta-glucose-1-phosphate (betaG1P) to beta-glucose-6-phosphate (G6P) catalyzed by beta-phosphoglucomutase (betaPGM) has been examined using steady- and presteady-state kinetic analysis. In the presence of low concentrations of beta-glucose-1,6-bisphosphate (betaG16BP), the reaction proceeds through a Ping Pong Bi Bi mechanism with substrate inhibition (kcat = 65 s(-1), K(betaG1P) = 15 microM, K(betaG16BP) = 0.7 microM, Ki = 122 microM). If alphaG16BP is used as a cofactor, more complex kinetic behavior is observed, but the nonlinear progress curves can be fit to reveal further catalytic parameters (kcat = 74 s(-1), K(betaG1P) = 15 microM, K(betaG16BP) = 0.8 microM, Ki = 122 microM, K(alphaG16BP) = 91 microM for productive binding, K(alphaG16BP) = 21 microM for unproductive binding). These data reveal that variations in the substrate structure affect transition-state affinity (approximately 140,000-fold in terms of rate acceleration) substantially more than ground-state binding (110-fold in terms of binding affinity). When fluoride and magnesium ions are present, time-dependent inhibition of the betaPGM is observed. The concentration dependence of the parameters obtained from fitting these progress curves shows that a betaG1P x MgF3(-) x betaPGM inhibitory complex is formed under the reaction conditions. The overall stability constant for this complex is approximately 2 x 10(-16) M(5) and suggests an affinity of the MgF3(-) moiety to this transition-state analogue (TSA) of < or = 70 nM. The detailed kinetic analysis shows how a special type of TSA that does not exist in solution is assembled in the active site of an enzyme. Further experiments show that under the conditions of previous structural studies, phosphorylated glucose only persists when bound to the enzyme as the TSA. (Abs. trunc. at 2000 ch.)
Descriptors		CRYSTALLOGRAPHY, X-RAY ENZYME INHIBITORS FLUORIDES GLUCOSEPHOSPHATES KINETICS MAGNESIUM COMPOUNDS MOLECULAR STRUCTURE PHOSPHOGLUCOMUTASE PROTEIN BINDING