These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: The kinetics of glucose-fructose oxidoreductase from Zymomonas mobilis.
    Author: Hardman MJ, Scopes RK.
    Journal: Eur J Biochem; 1988 Apr 05; 173(1):203-9. PubMed ID: 3356190.
    Abstract:
    Glucose-fructose oxidoreductase operates by a classic ping-pong mechanism with a single site for all substrates: glucose, fructose, gluconolactone and sorbitol. The Km values for these substrates were determined. The values of kcat are 200 s-1 and 0.8 s-1 for the forward and reverse directions respectively. The overall catalytic process consists of two half-reactions with alternate reduction of NADP+ and oxidation of NADPH tightly bound to the enzyme. Reduction of enzyme-NADP+ by glucose and oxidation of enzyme-NADPH by gluconolactone involve single first-order processes. The values of the rate constants at saturating substrate are 2100 s-1 and 8 s-1 respectively; deuterium isotope effects indicate that these are for the hydrogen transfer step. Oxidation of enzyme-NADPH by fructose is first order with a limiting rate constant of at least 430 s-1. The reaction of enzyme-NADP+ with sorbitol is biphasic, with rate constants for both phases less than 1 s-1. This behaviour is explained by a mechanism in which the slow cyclisation of the acyclic form of fructose follows its dissociation from the enzyme. The rate-determining steps for the overall reaction are probably dissociation of gluconolactone in the forward direction and hydrogen transfer from sorbitol to enzyme-bound NADP+ in the reverse direction.
    [Abstract] [Full Text] [Related] [New Search]