substrate inhibition

sub·strate in·hi·bi·tion

inhibition of an enzyme activity by a substrate of the reaction catalyzed by that enzyme; often, this type of inhibition occurs at elevated substrate concentrations in which the substrate is binding to a second, non-active site on the enzyme.
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For the determination of the kinetic mechanism with GSSG as the substrate, concentrations up to 60 [micro]M of the disulfide were used in order to avoid the strong substrate inhibition observed at moderate or high concentrations of GSSG.
This is due to some advantages presented by SSF, as follows (Singhania et al., 2010): the enzymes are produced by microorganisms directly on substrates insoluble in water that makes easier their recovery; the enzymes produced in SSF are less susceptible to substrate inhibition problems and present higher stability to temperature and pH variations.
GraphPadPrism 5 software was used to calculate regressions, including allosteric kinetics ([V.sub.0]= Vmax*[S]h/(K+ [S]h), where h is the Hill slope, MichaelisMenten ([V.sub.0] = Vmax*[S]/(Km + [S]) and MM with substrate inhibition ([V.sub.0]=Vmax*[S]/(Km + [S]*(1 + [S]/Ki).
fervidus enzymes show substrate inhibition at very low sulfopyruvate concentrations (100 [micro]M, i.e., 2.5-fold or 1.4-fold the sulfopyruvate [K.sub.M] values of these enzymes, resp.) [11].
The kinetic models Michaelis-Menten equation and substrate inhibition equation were fitted to the data of metabolic rates versus substrate concentrations and displayed in (1) and (2), respectively.
The natural of cephalosporin C acylase catalyzed the CPC to 7-ACA directly in a very low efficiency (14,15,16), significant substrate inhibition (14), and product inhibition (14).
The two binding sites have been used to explain the activation and substrate inhibition and biphasic saturation curves for the cytochrome P450 enzymes [52].
They used some kinetic models including substrate inhibition to determine the biokinetic parameters; the results were [[mu].sub.max] = 0.21 [h.sup.-1] and [q.sub.max] = 144 mmol/[g.sub.cell]/h with CO inhibitory effects on cell growth ([P.sup.L.sub.CO] > 60 kPa) and gas uptake ([P.sup.L.sub.CO] > 80 kPa).
This is consistent with work that demonstrated substrate inhibition via an allosteric binding site (Zhang et al.
[6, 7], in which case [[alpha].sub.1] = [V.sub.max], [[beta].sub.0] = [K.sub.m] and [[beta].sub.1] = 1, if p =1 and q = 2 (2) corresponds to a substrate inhibition model [8] and if p = q = 2 (2) can be interpreted in terms of an allosteric mechanism [4, 9].