What is the true enzyme kinetics in the biological system? An investigation of macromolecular crowding effect upon enzyme kinetics of glucose-6-phosphate dehydrogenase

Enzyme kinetic parameters for rate equations are vital in metabolic network simulation, a major part of systems biology research efforts. Measurements of Michaelis-Menten kinetic parameters K-m and K-cat have been performed for enzymes glucose-6-phosphate dehydrogenase (G6P DH) under crowded conditions using molecular crowding agents bovine serum albumin (BSA) and polyethylene glycol (PEG) of 8000 Da molecular weight. An increase in K-cat was observed at very low concentrations of crowding agent, and also at high crowder concentrations when the experiment was performed at 45 degrees C with PEG. The observed pattern in K-cat for G6P DH at high crowder concentrations has been explained via modelling using excluded volume theory. An increase in rate was observed at 45 degrees C for G6P DH versus 30 degrees C; this has been modelled via the Arrhenius equation. (C) 2011 Elsevier Inc. All rights reserved.