Michaelis-Menten constant solute effects

The peroxidase activity of immobilized catalase on the oxidation of phenol has been studied. The immt ilization was carried out from catalase solutions with pH < 3,5 on two kinds of soot differing in the average size of the particles building them up. The effect of the initial concentration of ph iol on the rate of its peroxidase oxidation by catalase immobilized on the soot of finer-graWd structure has been studied. The relationships obtained are described by the equation of Michaelis-Menten. The kinetic parameters (the constant of Michaelis - Km. the maximum reaction rate - V, the rate constant - k and the activation energy - of the process were calculated. It was found that catalase adsorbed on the soot of larger globular particles does not take part in the peroxidase oxidation of phenol. 

The distinction between the two kinds of direct coupling between transport and chemical reaction does not apply to secondary active transport, as the coupled processes are both vectorial. This transport is assumed to involve a ternary complex, i.e. between the translocator (carrier), the transportable solute and the co-ion. The latter is assumed to influence the translocation of the solute in two ways [25] (1) it may favor the formation of the ternary complex, in that its binding to the translocator increases the affinity of the latter to the transportable solute and vice versa (affinity effect) or, (2) it may increase the velocity at which the solute is translocated through the barrier, e.g. in that the ternary complex moves faster across the barrier than do the two binary complexes (velocity effect). In natural systems both effects appear to occur, separately as well as mixed. A crude distinction is often attempted on the basis of the two Michaelis-Menten parameters the maximum velocity V ) and the half saturation constant (A ) in the assumption that the former is altered in the velocity effect (V-type) and the latter, in the affinity effect (K-type). The relationship is often more complicated especially if electric potentials are involved [26]. 

The curve in Figure 8 is the equation and the points are the data derived from the reduction of the data in the inset of the figure. The activity constants derived from the Michaelis-Menten equation are Vmax = 0.11 nmol-min and Km = 0.1 mM. The spectrophotometric assay values of GUS in solution are Vmax == 1.55 nmohmin, and Km = 0.078 mM. The velocity maximum value for the immobilized enzyme is about 1/10 the value of the solution assay value (/P), probably due to the immobilization in the PSi surface framework restricting access to the enzymatic sites, effectively reducing the concentration of the available enzyme. The Km values, however, are similar, indicating the activity of the enzyme is not affected by the immobilization. 

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