Liver Alcohol Dehydrogenase. I. Kinetics and Equilibria without Inhibitors.

Publisher Website
Google Scholar
Abstract
Liver alcohol dehydrogenase can form the four binary complexes possible with DPNH, DPN, aldehyde and alcohol. The ternary complexes E-DPNH-aldehyde and E-DPN-alcohol are formed and are in very rapid equilibrium with one another. From a kinetic point of view the "Theorell-Chance" mechanism was nevertheless found to obtain. This depends on the following conditions: (1) The "on" velocity constants for DPNH and DPN are nearly independent of whether the enzyme is free or already combined with the substrate reaction partner. (2) The ternary complexes are in rapid equilibrium. (3) The ternary complexes prefer to liberate the substrate first, because this is less tightly bound than the coenzyme. The dissociation velocity of the binary enzyme-coenzyme complexes in the last phase of the reaction therefore becomes rate limiting when both substrate and coenzyme are present in high concentration in the first phase. (4) Determinations of initial reaction velocities with varied concentrations of both coenzyme and substrates have given Dalziel [PHI]-relations which agree with the specific requirements of the T. -C. -mechanism at pH 7. The values of the Michaelis constants close to zero concentration of their reaction partner, gave the dissociation constants Ke,R,Ke, O, KE, ald and Ke, alc.
Keywords