ISSN:
0006-3592
Keywords:
dual limitation
;
cofactor responses
;
kinetics
;
multiplicative model
;
structured model
;
Chemistry
;
Biochemistry and Biotechnology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
A structured model of substrate-utilization kinetics that encompasses dual-limitation conditions, caused by simultaneously low concentrations of the electron donor and the electron acceptor, is developed by incorporating the internal cofactor responses into the kinetic variables. The structured model is based on an assumption that the maximum specific electron-donor-oxidation rate (qmd) is not a constant, but is linearly controlled by the intracellular chemical potentials, log(NAD/NADH) and log(ATP/ADP · Pi). Determination of the kinetic parameters for the dual-limitation model, using experimental data from the companion article, verifies that qmd varies and demonstrates that the NAD/NADH ratio affects qmd in a positive direction; thus, an increase of the ratio increases the rate of electron-donor utilization. Because the internal NAD/NADH ratio rises with an increase in Sar the specific electron-donor-utilization rate is accelerated by high Sa. Since the ratio also increases as the specific electron-donor-utilization rate falls, the specific rate is intrinsically accelerated by the cofactor response when it becomes low due to a depletion of electron donor. Because the cofactor responses upon changes of the external substrate concentrations are systematic, the dual-limitation model can be expressed as a function of only external concentrations of electron donor and electron acceptor, which results in a multiplicative (double-Monod) form. Thus, dual limitation by both substrates reduces the overall reaction rate below the rate expected from single limitation by only one, the most severely limiting, substrate. © 1996 John Wiley & Sons, Inc.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
