Enzyme kinetics highly reversible systems

Kinetic studies of several ADP-Glc PPases show that the presence of the activator in reaction mixtures usually lowers the concentration of the substrates, ATP, Glc-l-P, pyrophosphate ADP-Glc, and the cationic activator Mg + (or Mn +), required for 50% of maximal velocity K or Sq ) about 2-15-fold. The apparent affinity of the enzyme for the substrate is thus increased in the presence of the activator. The activator also increases maximal velocity and 2- to 60-fold depending on the pH and the particular ADP-Glc PPase studied. The prime function of the allosteric activator may be, however, to reverse the sensitivity of the enzyme to inhibition by P AMP, or ADP, which are usually noncompetitive with the substrates. Indeed, for many ADP-Glc PPases, relatively high concentrations of the activator can completely reverse the inhibition caused by AMP, Pj, or ADP. A well-studied system is the E. coli B enzyme, where fructose-1,6-bisphosphate modulates the sensitivity to AMP inhibition. ° The /0.5 (concentration giving 50% inhibition) for 5 -AMP is about 75 pmoll at 1.7 mmolH fructose-1,6-bisphosphate. With lower concentrations of the activator, however, the... 

The real potential of membrane reactors becomes evident with coenzyme dependent enzymatic systems.10 20 21 Coenzymes, like NAD+ or NADP+, usually have a long term effect on enzyme activity only if they can move from one enzyme, able to oxidize them, to another, able to reduce them, in loop kinetics. Continuous homogenous catalysis is then a prerequisite to achieving high reaction yields. Enzyme membrane reactors offer a suitable reaction environment provided that coenzymes are retained in the reaction system. Such compounds are in fact quite expensive, which limits the use of coenzyme dependent enzymes. Reverse osmosis (RO) membranes could be helpful in retaining native... 

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