Substrate and product inhibition

Substrate and product inhibitions analyses involved considerations of competitive, uncompetitive, non-competitive and mixed inhibition models. The kinetic studies of the enantiomeric hydrolysis reaction in the membrane reactor included inhibition effects by substrate (ibuprofen ester) and product (2-ethoxyethanol) while varying substrate concentration (5-50 mmol-I ). The initial reaction rate obtained from experimental data was used in the primary (Hanes-Woolf plot) and secondary plots (1/Vmax versus inhibitor concentration), which gave estimates of substrate inhibition (K[s) and product inhibition constants (A jp). The inhibitor constant (K[s or K[v) is a measure of enzyme-inhibitor affinity. It is the dissociation constant of the enzyme-inhibitor complex. 

The batch experiment had neither incoming fresh media nor any product stream leaving the fermentation vessel. A complete experimental set up with a B. Braun Biostat, is shown in the above laboratory experimental set up. The continuous flow of media requires a feed tank and product reservoir. The batch process has many disadvantages such as substrate and product inhibition, whereas in the continuous process the fresh nutrients may remove any toxic by-product formed. 

Robustness of the process. Many transition metal-catalyzed reactions function well at the laboratory scale, but on scaling up substrate and product inhibition may be an issue, and sensitivity to impurities may also become apparent. Increasing the SCR, which is often necessary for the economics of the process, also increases the impurity catalyst ratio. It is also very important to keep the number of components to a minimum, as extraction, crystallization and distillation are the only economic means of purification. Ligands can be a nuisance in this respect, particularly if they are used in amounts over 5 mol%. Reproducibility also is a stringent requirement. Thus, possible inhibition mechanisms should be recognized in order to avoid unwanted surprises during production. 

Substrate and product inhibition. Few academic researchers are familiar with this phenomenon as they usually mn their hydrogenations at low substrate concentrations and low SCR. However, for industrial applications the space-time yield of a reaction - the amount of product per unit reactor volume per time unit - is quite important. Clearly, the higher the substrate concentration the higher the space-time yield and the more economic the process. More often than not, either substrate or product inhibition becomes a problem when the substrate concentration is increased to 10 wt% or more. 

Integrated Michaelis-Menten Equation for Substrate and Product Inhibition... 

Van Niel Ed, W. J., Claasen Pieternel, A. M., and Stams Alfons, J. M. 2003. Substrate and product inhibition of hydrogen production by the extreme thermophile, Caldi-cellulosiruptor saccharolyticus. Biotechnol. Bioeng.,81,255-262. 

For Baeyer-Villiger oxidations of ketones into lactones, recombinant whole-cell catalysts were constructed using the CHMO from A. calcoaceticus and cells of S. cerevisiae [127-129] or E. coli [130-132] as host system. These designer cells were used for example for the biotransformation of bicyclo[3.2.0]-hept-2-ene-6-one [133-136], In order to avoid the substrate and product inhibition, an adsorber... 

Although the parameters governing a whole cell-based process are numerous, the key limitation of the low productivity was clearly idenhfied as substrate and product inhibition. Substrate inhibition could conveniently be overcome by continuous feeding. A pilot-scale fed-batch experiment (551) was carried out [101] in which the feeding rate was adjusted to maintain the ketone concentrahon below 0.7 g/1. A final concentration of about 4g/l of lactones was reached within 4h. After downstream product recovery on charcoal, over 200 g of combined lactones was obtained, corresponding to a 76% yield. 

Unfortunately, most enzymes do not obey simple Michaelis-Menten kinetics. Substrate and product inhibition, presence of more than one substrate and product, or coupled enzyme reactions in multi-enzyme systems require much more complicated rate equations. Gaseous or solid substrates or enzymes bound in immobilized cells need additional transport barriers to be taken into consideration. Instead of porous spherical particles, other geometries of catalyst particles can be apphed in stirred tanks, plug-flow reactors and others which need some modified treatment of diffusional restrictions and reaction technology. 

All the nitrile hydrolyzing enzymes described so far are intracellular and differ considerably with respect to substrate specificity, stereoselectivity, molecular mass and substrate and product inhibition characteristics. 

An enzymatic acrylonitrile hydration was first patented in 1981 8nitrile hydratases of different origin have been shown to be able to convert acrylonitrile into acrylamide. However, a major problem associated with biocatalysis for production of acrylonitrile is the short half-life of the enzyme due to substrate and product inhibition. Acrylonitrile is a strong alkylating agent which reacts by Michael addition with the sulfhydryl groups of proteins f 8, 69L... 

The utilization of glucose and fnictose into ethanol uses the Levenspiel toxic inhibition equation for ethanol production [6]. This was used after more complex rate expressions including both substrate and product inhibition failed to improve model performance evidenced by failing to decrease the cost function. 

Pan JL, Syu MJ (2(X)5) Kinetic study on substrate and product inhibitions for the formation of 7-amino-3-deacetoxy cephalosporanic acid from cephalosporin G by immobilized penicillin acylase. Biochem Eng J 23 203-210... 

ALT catalyzes the reaction (reaction [VII]), and the pyruvate formed is reduced by NADH in a reaction catalyzed by LDH (indicator reaction, reaction [VIII]). The activity is measured by monitoring the decrease in absorbance of 340 nm due to the oxidation of NADH. The substrate concentrations are optimized theoretically, based on the kinetics of a two-substrate inhibited reaction because the ALT is subject to both substrate and product inhibitions. 

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