Maximum reaction velocity apparent

Lineweaver-Burk plotting was performed for the immobilized enzymes with different spacers. The Michaelis constant Km and the maximum reaction velocity Vm for the free and the immobilized LPL on PAM microspheres are tabulated in Table 2, together with those of the ChB-N(2 -papain series. The apparent Km of the immobilized LPL without spacer was higher than that of the immobilized LPL with spacer and the free one. This may be because the probability of formation of LPL-substrate complex will decrease for the LPL immobilized without spacer owing to the steric hindrance, compared with those of the enzymes with spacer and the free one. On the other hand, the Vm value of LPL immobilized without spacer gives the lowest value, suggesting that the relative activity of the directly immobilized LPL decreased in the course of the covalent fixation. 

For GOD, apparent Michaelis-Menten constants K, the substrate concentration at which the reaction velocity is half the maximum velocity, Vmaxl l) ranging from 4 mM to 13 mM have been cited for different immobilization conditions [36]. In excess glucose (i.e, glucose concentrations sufficiently greater ), the rate of hydrogen peroxide generation can be approximated by... 

In ester synthesis and exchange reactions, as well as in hydrolysis re tions induced by PEG-lipase in hydrophobic media, the existence of a trace amount of water in the reaction system was most important in terms of the reactions proceeding. Matsushima et al. [67] carried out a kinetics study of PEG-lipase in transparent benzene solution to estimate the value of water, one of the substrates of lipase in the ester hydrolytic reaction. Indoxyl acetate was hydrolyzed by PEG-lipase to form acetic acid and 3-hydroxyindole, which was photometrically determined. A double-reciprocal plot of the velocity of the indoxyl acetate hydrolysis against water concentration at a given concentration of indoxyl acetate indicated that the hydrolysis took place as a double-displacement reaction (ping-pong reaction). The apparent Michaelis-Menten constant of water and the maximum velocity were calculated to be = 7 X 10 M and Vmax = 4700 xmol/min/mg of protein, respectively. 

The immobilization procedure may alter the behavior of the enzyme (compared to its behavior in homogeneous solution). For example, the apparent parameters of an enzyme-catalyzed reaction (optimum temperature or pH, maximum velocity, etc.) may all be changed when an enzyme is immobilized. Improved stability may also accrue from the minimization of enzyme unfolding associated with the immobilization step. Overall, careful engineering of the enzyme microenvironment (on the surface) can be used to greatly enhance the sensor performance. More information on enzyme immobilization schemes can be found in several reviews (7,8). 

An enzyme is said to obey Michaelis-Menten kinetics, if a plot of the initial reaction rate (in which the substrate concentration is in great excess over the total enzyme concentration) versus substrate concentration(s) produces a hyperbolic curve. There should be no cooperativity apparent in the rate-saturation process, and the initial rate behavior should comply with the Michaelis-Menten equation, v = Emax[A]/(7 a + [A]), where v is the initial velocity, [A] is the initial substrate concentration, Umax is the maximum velocity, and is the dissociation constant for the substrate. A, binding to the free enzyme. The original formulation of the Michaelis-Menten treatment assumed a rapid pre-equilibrium of E and S with the central complex EX. However, the steady-state or Briggs-Haldane derivation yields an equation that is iso-... 

Figure 13. Cartesian [center-of-mass (CM)] contour diagrams for NH+ produced from reaction of N+ with H2. Numbers indicate relative product intensity corresponding to each contour. Direction of N+ reactant beam is 0° in center-of-mass system. For clarity, beam profiles have been displaced from their true positions (located by dots and 0°). Tip of velocity vector of center of mass with respect to laboratory system is located at origin of coordinate system (+). Scale for production velocities in center-of-mass system is shown at bottom left of each diagram (a) reactant N+ ions formed by impact of 160-eV electrons on N2 two components can be discerned, one approximately symmetric about the center of mass and the other ascribed to N+(IZ3), forward scattered with its maximum intensity near spectator stripping velocity (b) ground-state N+(3/>) reactant ions formed in a microwave discharge in N2. Only one feature is apparent—contours are nearly symmetric about center-of-mass velocity.12 ...

The catalytic efficiency of an enzyme is indicated by its kcatIKM value, the value combining the effectiveness of both the productive substrate binding and the subsequent conversion of substrate molecules into product (Copeland, 2000). This value is the apparent second-order rate constant for enzyme action under conditions in which the binding site of the enzyme is largely unoccupied by substrate. The kcatIKM value is the index for comparing the relative rates of cleavage of alternative, competing substrates. The KM is the Michaelis constant, an apparent dissociation constant and hence a measure of substrate affinity. This value equals the concentration of substrate needed to reach half maximum velocity of the enzyme reaction. 

The apparent increase in rate may arise from the increase in surface as carbon was removed from the original particle. Although the conventional experimental rate equation for the carbon-steam reaction (6) states that steam is a part of the rate equation, it further states that steam also inhibits the rate. The test procedure used here maintains inlet steam at a fixed velocity and in large excess thus any effect of the level of steam conversion should be negligible on the integral rates calculated here. In the runs shown in Figure 2, the maximum use of steam by carbon in a 5-min. period varied from 3.6 to 8.5% of the total steam available. Of... 

Maximum velocities for the reaction of bromoacetyl derivatives of A-U-G and of TJ-G-A with Escherichia coli 70 S ribosomes have been determined to be 5 X 10" mole-sec". The Km values of the A-U-G and of the U-G-A label, on the other hand, differ by 20-fold. This difference in apparent affinity seems to be without influence on the maximum veloc-... 

Inorganic Anions. Inorganic anions, most notably chloride, severely inhibit PEP carboxylase (Osmond and Greenway, 1972). The inhibition is most severe when the reaction is run at the apparent PEP Km. Detailed studies show that the theoretical maximum velocity for the reaction is not significantly affected, but the apparent Km for PEP is increased as much as four fold in the presence of 100 mM NaCl. Hence, it appears that chloride interferes with the binding of PEP to the enzyme (Table 4.5). 

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