Abstract
The conjugated enzyme system of NAD kinase (NK) and acetate kinase (AK) was investigated to produce NADP continuously by the dynamic recycling of ATP. The enzymes were physically entrapped in an ultranltration hollow fiber tube and the cosubstrate, ATP, as well as the substrates were fed to the reactor continuously. The ATP turnover increased with a decrease in the concentration of ATP fed and with an increase in the concentration of immobilized enzymes. The maximal productivity of the reactor was 0.228 μmol/hr/ml-reactor with an ATP turnover of 8.35. The experimental results were approximately predicted using a theoretical model in which the equilibrium random mechanism was assumed for the AK reaction and neglecting the backward reaction for NK. When the concentration of ATP fed was much lower than the Michaelis constant of NK for ATP, the ATP turnover took a constant value irrespective of the ATP feed concentration, and this value was proportional to the concentration of NK. A rate limiting step was proved to exist in the reaction of NK. The half-life of the enzyme system was over 10 days in a continuous operation.
