Enzymes effect upon reaction rate

The volumetric ratio of the two liquid phases (j6 = Forg/ Faq) can affect the efficiency of substrate conversion in biphasic media. The biocatalyst stability and the reaction equilibrium shift are dependent on the volume ratio of the two phases [29]. In our previous work [37], we studied the importance of the nonpolar phase in a biphasic system (octane-buffer pH 9) by varying the volume of solvent. The ratio /I = 2/10 has been the most appropriate for an improvement of the yield of the two-enzyme (lipase-lipoxygenase) system. We found that a larger volume of organic phase decreases the total yield of conversion. Nevertheless, Antonini et al. [61] affirmed that changes in the ratios of phases in water-organic two-phase system have little effect upon biotransformation rate. 

Confidence intervals (Equation 10.66) suggest that it is unlikely the sodium ion concentration has a statistically significant effect upon the rate of the enzyme catalyzed reaction some other factor, one that is correlated with time, is probably responsible for the observed effect (see Section 1.2 on masquerading factors). 

A reaction which follows power-law kinetics generally leads to a single, unique steady state, provided that there are no temperature effects upon the system. However, for certain reactions, such as gas-phase reactions involving competition for surface active sites on a catalyst, or for some enzyme reactions, the design equations may indicate several potential steady-state operating conditions. A reaction for which the rate law includes concentrations in both the numerator and denominator may lead to multiple steady states. The following example (Lynch, 1986) illustrates the multiple steady states... 

Apparent Temperature Optimum. A rise in temperature has a dual effect upon an enzyme-catalyzed reaction it increases the rate of the reaction, but it also increases the rate of thermal inactivation of the enzyme itself. Like the pH optimum, the temperature optimum may in certain instances be altered by environmental conditions, e.g., pH, type and strength of buffer, etc. The term temperature optimum, therefore, is useless unless the incubation time and other conditions are specified. A more enlightening term is apparent temperature optimum, which indicates that the optimum has been obtained under a... 

The reasons for the effect of pH upon the catalytic properties of enzymes are numerous and will not be discussed here. For most enzymes, however, there is a pH at which they are optimally effective changing the pH to lower (more acidic) levels or to higher (more basic) levels will decrease the overall rate at which the associated chemical reaction occurs. In the region of the optimum pH, the reaction rate vs. pH response surface can usually be approximated reasonably well by a second-order, parabolic relationship. 

Based upon this information, the researcher would probably conclude that the concentration of sodium ion does have an effect on the rate of the enzyme catalyzed reaction. However, this conclusion might be wrong because of the lurking presence of a highly correlated, masquerading factor, time (see Section 1.2). 

During (he measurement of die enzyme reaction, the reaction velocity ideally should remain constant. Case of proteases or hydrolases ate known where the reaction rate gradually decreases as a result of an inhibitory effect of the reaction products, Therefore it is recommended that an enzyme assay be based, when feasible, upon a measurement of the initial reaction rate. This initial reaction rate can in most cases be obtained by extrapolation, a minimum reaction time being required for obtaining a sufficiently precise titration of the molecules removed or produced during this fixed time span. 

Kinetics of Immobilized Enzymes. Another major factor in the performance of immobilized enzymes is the effect of the matrix on mass transport of substrates and products. Hindered access to the active site of an immobilized enzyme can affect the kinetic parameters in several ways. The effective concentration of substrates and products is also affected by the chemistry of the matrix especially with regard to the respective partition coefficients between the bulk solution and the matrix. In order to understand the effects of immobilization upon the rate of an enzyme-catalyzed reaction one must first consider the relationship between the velocity of an enzyme-catalyzed reaction and the... 

Adenylate cyclase is considered as a second messenger that catalyzes the formation of cAMP (cyclic adenosine monophosphate) from ATP this results in alterations in intracellular cAMP levels that change the activity of certain enzymes—that is, enzymes that ultimately mediate many of the changes caused by the neurotransmitter. For example, there are protein kinases in the brain whose activity is dependent upon these cyclic nucleotides the presence or absence of cAMP alters the rate at which these kinases phosphorylate other proteins (using ATP as substrate). The phosphorylated products of these protein kinases are enzymes whose activity to effect certain reactions is thereby altered. One example of a reaction that is altered is the transport of cations (e.g., Na+, K+) by the enzyme adenosine triphosphatase (ATPase). 

The detrimental effects of these enzyme-mediated chemical reactions upon dietary nitrogen should be manifested in insects such as H. zea and S. exigua initially as reduced growth rate and subsequently as potentially detrimental effects on life-history traits (e.g., longevity, fecundity, and survivorship)(97,98). 

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