title: Steady-state kinetics of coupled two-enzyme reactor with recycling of poly(ethylene glycol)-bound NAD.
abstract: The kinetic properties of a continuous enzyme reactor containing rabbit muscle lactate dehydrogenase, horse liver alcohol dehydrogenase and poly(ethylene glycol)-bound NAD (PEG-NAD) were investigated experimentally and theoretically. The enzymes and PEG-NAD were retained in the reactor with an ultrafiltration membrane, and the substrates (pyruvate and ethanol) were fed continuously. The reactions of the dehydrogenases were coupled by the recycling of the cofactor. The steady-state concentration of L-lactate, one of the products, was measured under different experimental conditions and compared with the corresponding theoretical value. The theoretical value was calculated based on a simplified ordered bi-bi mechanism for the individual enzyme reactions, of which kinetic constants were determined by independent kinetic studies. Differences were found between the kinetic constants of the enzymes for NAD(H) and PEG-NAD(H). The steady-state values obtained by continuous operation were lower than those calculated, possibly due to the simplification made for the kinetic model; but there was general agreement between them in the dependence on the experimental conditions. The steady-state behavior of the enzyme reactor was explained semi-quantitatively by the simple kinetic model.
mesh_terms: D000426:Alcohol Dehydrogenase; D000429:Alcohol Oxidoreductases; D000818:Animals; D006736:Horses; D007700:Kinetics; D007770:L-Lactate Dehydrogenase; D008099:Liver / Q000201:enzymology; D008956:Models, Chemical; D009132:Muscles / Q000201:enzymology; D009243:NAD; D011092:Polyethylene Glycols; D011817:Rabbits
chemical_list: D009243:NAD; D011092:Polyethylene Glycols; D000429:Alcohol Oxidoreductases; D000426:Alcohol Dehydrogenase; D007770:L-Lactate Dehydrogenase