Specific activity constant

The dinitrophenylhydrazones were separated from the reaction mixture by thin-layer chromatography (silica gel G developed with benzene) and further purified by thin-layer chromatography on aluminum oxide G (petroleum ether-diethyl ether (96 to 4), silica gel G (chloroform), and silica gel G (diethyl ether)). In all cases, the specific activities of the dinitrophenylhydrazones remained constant over the course of the last two purifications. 

It is necessary to note the limitation of the approach to the study of the polymerization mechanism, based on a formal comparison of the catalytic activity with the average oxidation degree of transition metal ions in the catalyst. The change of the activity induced by some factor (the catalyst composition, the method of catalyst treatment, etc.) was often assumed to be determined only by the change of the number of active centers. Meanwhile, the activity (A) of the heterogeneous polymerization catalyst depends not only on the surface concentration of the propagation centers (N), but also on the specific activity of one center (propagation rate constant, Kp) and on the effective catalyst surface (Sen) as well ... 

Michaelis constant K for D-glyca] hydration. Approximate value calculated from specific activity with M, 50,000. 

Figure 2 show that the specific activity fi om the cotyledons (mean value 38,200 and 13,900 dpm mg protein at pH 5.5 and 7 repectively) was also larger than from hypocotyls (21,300 and 7,500) or roots (18,600 and 10,500). Whatever the pH, two peaks occured in the cotyledons (days 3 and 9) while the specific activity was slightly increasing in the roots, during the culture. In the hypocotyls, the activity was rather constant at pH 5.5 and presented two peaks at neutral pH. In all cases, the specific activity was larger than that of suspension-cultured cells which had been estimated in the range of 250 and 2500 dpm mg" protein. 

The mass activity MA (in A g ) of the Pt catalyst is, of course, the product of the specific activity js (in A m ) and the specitic surface area 5mass (in ni g ) MA = js mass- Because S ass is inversely proportional to the particle diameter dpt, the use of supported Pt nanoparticles is effective for increasing MA, if js is a constant independent of dpt- However, even at pure Pt, conflicting results on the values of js and P(H202) have been reported, suggesting the presence of differences in electrochemical properties between bulk and supported nanoparticles. For example, Bregoli [1978]... 

B, the initial rate constants are diminished, in contrast to those observed for the catalytic system (61). The reasons for the different effects of protein B on the two reactions with Hox are unknown. With Hox from M. capsulatus (Bath), activities of only —10% of the values observed under optimal catalytic conditions were found with the H202 shunt pathway, assuming specific activities to be greater than 200 mU/mg (59). As a consequence of the poor yields observed, the effect of protein B on the system was not investigated further. 

If the activity coefficients are assumed to be unity, the specific rate constant k is then identical to k K. It can be shown that... 

Table 2. Copolymerization constants (r, and r2), specific activities (Q2) and polarities (e2) for MA-TASM pairs219 ...

From the experimental results at low conversions 10%), copolymerization constants, specific activities (Q) and polarities (e) were determined for the monomer pairs under study. The values obtained were as follows ... 

First-order rate constants are used to describe reactions of the type A — B. In the simple mechanism for enzyme catalysis, the reactions leading away from ES in both directions are of this type. The velocity of ES disappearance by any single pathway (such as the ones labeled k2 and k3) depends on the fraction of ES molecules that have sufficient energy to get across the specific activation barrier (hump) and decompose along a specific route. ES gets this energy from collision with solvent and from thermal motions in ES itself. The velocity of a first-order reaction depends linearly on the amount of ES left at any time. Since velocity has units of molar per minute (M/min) and ES has units of molar (M), the little k (first-order rate constant) must have units of reciprocal minutes (1/min, or min ). Since only one molecule of ES is involved in the reaction, this case is called first-order kinetics. The velocity depends on the substrate concentration raised to the first power (v = /c[A]). 

The turnover number, or kCM (pronounced kay kat ), is another way of expressing Vmax. It s Vmax divided by the total concentration of enzyme (Vmax/E,). The kcat is a specific activity in which the amount of enzyme is expressed in micromoles rather than milligrams. The actual units of kcat are micromoles of product per minute per micromole of enzyme. Frequently, the micromoles cancel (even though they re not exactly the same), to give you units of reciprocal minutes (min-1). Notice that this has the same units as a first-order rate constant (see later, or see Chap. 24). The kcat is the first-order rate constant for conversion of the enzyme-substrate complex to product. For a very simple mechanism, such as the one shown earlier, kcat would be equal to k3. For more complex... 

Another cultured cell line of Catharanthus roseus (EU4A), which does not produce detectable amounts of vinblastine and other bisindole alkaloids, was also examined for its ability to transform 78 (183). Cell-free extracts of the culture line were prepared, and the 35,000 X g supernatant solution was used. Incubations with 2r-tritioanhydiovinblastine yielded a mixture from which radioactive vinblastine (52) was isolated. The labeled vinblastine was reisolated after unlabeled carrier was added and rigorously purified by successive thin-layer chromatography, reversed-phase HPLC, and crystallization to constant specific activity. Boiled extracts could not produce labeled 52, thus supporting the involvement of enzymes in the conversion process. 

For those interested in the discovery of drug candidates to attenuate SSAO/ VAP-1 activity there are two properties that need to be considered. First, as mentioned above, SSAO/VAP-1 exists as a membrane bound protein and a truncated version is found in the plasma [10,11]. Second, there is tremendous species variation which is revealed in a very large range of the second order rate constant V/K, using benzylamine as substrate, [22,23], and that inhibitor potencies vary widely according to the species [24,25]. Furthermore, within a single species specific activity varies from tissue to tissue [26]. 

More complex forms of activity term rate laws involve various ions and complexes in solution. Dissolution and precipitation phenomena are in this approach regarded as a summation of individual reactions taking place at the surface of the solid. The net absolute rate is obtained as a summation of individual terms /, each with its specific rate constant k and activity product (Delany et al., 1986) ... 

With respect to an enzyme, the rate of substrate-to-product conversion catalyzed by an enzyme under a given set of conditions, either measured by the amount of substance (e.g., micromoles) converted per unit time or by concentration change (e.g., millimolarity) per unit time. See Specific Activity Turnover Number. 2. Referring to the measure of a property of a biomolecule, pharmaceutical, procedure, eta, with respect to the response that substance or procedure produces. 3. See Optical Activity. 4. The amount of radioactive substance (or number of atoms) that disintegrates per unit time. See Specific Activity. 5. A unitless thermodynamic parameter which is used in place of concentration to correct for nonideality of gases or of solutions. The absolute activity of a substance B, symbolized by Ab, is related to the chemical potential of B (symbolized by /jlb) by the relationship yu,B = RTln Ab where R is the universal gas constant and Tis the absolute temperature. The ratio of the absolute activity of some substance B to some absolute activity for some reference state, A , is referred to as the relative activity (usually simply called activity ). The relative activity is symbolized by a and is defined by the relationship b = Ab/A = If... 

The rates of all single-step reactions increase as the temperature increases. This may not be true for multistep reactions such as those involved with multistep polymerizations, here the cationic polymerization. For cationic polymerizations the activation energies are generally of the order > E > E. Remembering that the description of the specific rate constant is... 

The BPO decomposes with a specific rate constant of about 10 /sec, an Arrhenius constant (A) of about 10 , and an activation energy of about 28 kcal/mol (about 115 kJ/mol). As noted earlier, not all radicals initiate new chains. Some terminate prior to initiation forming inactive products, mainly phenyl benzoate (Equation 6.5). Thus, as noted, an efficiency constant (/) is used that reflects the ratio of BPO that actually form chains. 

Figure 7. Comparison between H-Beta zeolites (open circles and dashed lines) and HY zeolites (continuous lines) for gas-oil cracking (a) First-order activity constant by specific surface area vs, Si/Al ratio (b) and (c) Average total conversion vs. gas-oil ratio for a H-Beta with Si/Al=27 and a HY Si/Al=35, and for a H-Beta with Si/Al=10 and a Hy with Si/Al=7.7 respectively. Solid circles correspond to the H-Beta steamed at 750 C and 1 atmosphere of water pressure.

For lipase, initial activity corresponds to the amount of protein that was adsorbed. Specific activity is constant at 1 mmoFs gE for this carrier-enzyme system, which compares to 27% of the free enzyme activity. The trypsin system shows a lower specific activity that is only 10% of the free enzyme. The reason for the lower recovered activity of this system is not known. To rule out possible internal diffusion limitations, the Wheeler-Weisz modulus was estimated, assuming a carrier layer thickness of 0.1 mm for all carriers. Using the data of the experiments performed at 150 rpm, one finds ... 

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