Relative remaining activity

The relative remaining activity of alcohol dehydrogenase in an optimal water-ethanol mixture exceeded 100%. The observation of the improved activity of some of the enzyme samples after this procedure [179] was a precursor to later achievements on enzyme activation in organic media [178],... 

TABLE 1 Effect of Organic Solvents on Relative Remaining Activity of Thermolysin Immobilized onto XAD-7 and Solubility of Water... 

No. Organic solvent Relative remaining activity (%) Solubility of water" (g water/100 mL soL)... 

On the other hand, in water-immiscible organic solvents, there was a positive correlation between the relative remaining activity and remaining amount... 

FIG. 10 Relationship between relative remaining activity and relative remaining... 

With an increase in the water content in the bulk organic solvent, the A 2 [Eo] value appreciably increased, as shown in Table 2. The increased A 2 [Eo] values with an increase in the water content in the bulk organic solvent might be ascribed to the increased fraction of the aqueous phase in which the enzyme aggregates exist, which promoted autolysis. To test this speculation, the relative remaining activity after 5-h incubation at 70°C at 4% water content in the bulk organic solvent was plotted against the water content inside the support, for enzyme immobilized onto various supports in addition to Amberlite XAD-7 in ethyl acetate and in tert-amyl alcohol (Fig. 12) [59]. The values of... 

FIG. 12 Relationship between the relative remaining activity of thermolysins immobilized onto Amberlite XAD-7 [1,2], Amberlite XAD-8 [3], Amberlite XAD-5003 [4], and CPG-7.5 [5], and CPG-300 [6] and water content inside the immobilized enzyme after 5-h incubation at 70°C in ethyl acetate (open circles) and in ferf-amyl alcohol (closed circles). The figures in parentheses indicate the water content in the bulk organic solvent phase. (From Ref. 59.)... 

FIG. 13 Correlation of the relative remaining activity of the enzyme immobilized onto Amberlite XAD-7 with log P and Ej [30] values for water-miscible organic solvents. The numbers in the figure correspond to the kinds of organic solvents shown in Table 1. All the organic solvents contained 4% water. (From Ref. 59.)... 

In seawater, HCO3 ions lead to surface films and increased polarization. In aqueous solutions low in salt and with low loading of the anodes, less easily soluble basic zinc chloride [10] and other basic salts of low solubility are formed. In impure waters, phosphates can also be present and can form ZnNH4P04, which is very insoluble [11]. These compounds are only precipitated in a relatively narrow range around pH 7. In weakly acid media due to hydrolysis at the working anode, the solubility increases considerably and the anode remains active, particularly in flowing and salt-rich media. 

This equation is particularly useful to derive apparent estuarine water mass ages (Fig. 6) because the term /em is removed. Using ( Ra/ " Ra) isotope ratios in this manner is based on the assumption that the initial ( Ra/ " Ra) activity ratio must remain constant. This conclusion is reasonable as the long-lived parent isotopes ( Pa and Th) have relatively constant activity ratios in sediments, and the intermediate Th isotopes ( Th and Th) are scavenged efficiently in the near-shore water column. The utility of Ra as... 

The poisoning of the nickel surface is manifested in a sharp increase of electrode potential relative to the value in the active state. Since at most only part of the surface remains active, the actual current density can be much... 

The activities of NHases from Rhodococcus sp. Adpl2 and Gordonia sp. BR-1 strains have been partially characterized [25]. In reactions that catalyze the hydration of a-hydroxynitriles such as lactonitrile or glycolonitrile, the substrate can dissociate to produce HCN and the corresponding aldehydes. HCN can inhibit and/or inactivate NHase, and it was determined that these two enzymes remain active in the presence of cyanide ion at concentrations up to 20 him. The dependence of the NHase activity of cell-free extracts of Rhodococcus rhodochrous J1 and Gordonia sp. BR-1 on cyanide ion concentration is illustrated in Figure 8.1, demonstrating the improved cyanide stability of BR-1 NHase relative to that of Jl. 

Very rapid-acting paralytic neurotoxin that binds to sodium channels of nerve and muscle cells depolarizing neurons by increasing the sodium channel permeability. It is obtained from South American poison-dart frogs (Phyllobates aurotaenia, Phyllobates terribilis). It is insoluble in water but soluble in hydrocarbons and other nonpolar solvents. The dried toxin can remain active for at least a year. However, it is relatively nonpersistent in the environment. 

Various chromatographic techniques may be utilized to purify urokinase further. Commonly employed methods include anion-exchange (DEAE-based) chromatography, gel filtration on Sephadex G-100 and chromatography on hydroxyapatite columns. Urokinase is a relatively stable molecule. It remains active subsequent to incubation at 60 °C for several hours, or brief incubation at pHs as low as 1.0 or as high as 10.0. 

Most protein serine-threonine kinases undergo autophosphorylation. The autophosphorylation of most protein kinases is associated with an increase in kinase activity [4, 10]. In some instances, such as with the RII subunit of PKA, autophosphorylation represents a positive feedback mechanism for kinase activation, in this case by enhancing the rate of dissociation of the RII and C subunits. In the case of CaMKII, autophosphorylation causes the catalytic activity of the enzyme to become independent of Ca2+ and calmodulin. This means that the enzyme, activated originally in response to elevated cellular Ca2+, remains active after Ca2+ concentrations have returned to baseline. By this mechanism, neurotransmitters that activate CaMKII can produce relatively long-lived alterations in neuronal function. In other instances, such as with the receptor-associated protein tyrosine kinases (discussed in Ch. 24), autophosphorylation is an obligatory step in the sequence of molecular events through which those kinases are activated and produce physiological effects. 

In addition to the TDI experiment, the partition ratio measures the TDI efficiency. Specifically, the partition ratio is the number of inactivation kinetic events (k nact) versus the number of substrate turnover events per unit enzyme (kcat) [161], Thus, the most potent partition ratio is zero. The most common experimental setup for determining the partition ratio is the titration method that increases the inhibitor concentration relative to a known amount of enzyme. After the incubations, a secondary incubation containing a probe substrate similar to the TDI experiment is used to define the remaining activity. For accurate determination of the partition ratio from the titration method, it is assumed that the inhibitor is 100% metabolized ... 

In comparison, no structural modification of model B was seen before 120 h of aging (80 °C). However, after 120 h two small doublets appeared in the NMR spectrum and several additional peaks became noticeable in the NMR spectrum. It was determined by NMR and IR spectroscopy that the hydrolysis products were an imide/carboxylic acid and an imide/anhydride. Model B was then aged for 1200 h at 80 °C to quantitatively determine the amount of hydrolysis products as a function of time. The relative intensity of the peaks due to carboxylic acid is constant after some time. The authors suggest that an equilibrium occurs between model B and the products formed during hydrolysis, and therefore, the conversion to hydrolysis products is limited to about 12%. This critical fraction is probably enough to cause some degradation of polymeric materials, but research on six-membered polyimides has remained active. 

Since movement within the solvation shell in these complexes is relatively sluggish, it is postulated that a complex remains activated only long enough to react with its immediate environment, the inner solvation shell. In the reaction with anionic species, a situation can be reached in which nearly all of the substrate is in the form of the maximum ion aggregate. Any increase in the anion concentration in the bulk solvent will not change the immediate environment of nearly all the substrate and, therefore, will not effect the reaction rate. In this way a limiting rate can be independent of the concentration of added anionic reagent, irrespective of the actual mechanism of the actual act of substitution. 

Esters are widespread in fruits and especially those with a relatively low molecular weight usually impart a characteristic fruity note to many foods, e.g. fermented beverages [49]. From the industrial viewpoint, esterases and lipases play an important role in synthetic chemistry, especially for stereoselective ester formations and kinetic resolutions of racemic alcohols [78]. These enzymes are very often easily available as cheap bulk reagents and usually remain active in organic reaction media. Therefore they are the preferred biocatalysts for the production of natural flavour esters, e.g. from short-chain aliphatic and terpenyl alcohols [7, 8], but also to provide enantiopure novel flavour and fragrance compounds for analytical and sensory evaluation purposes [12]. Enantioselectivity is an impor-... 

The effects of these agents can persist for hours or days after the agonist concentration has been reduced to zero. The persistence of effect is primarily due to the relatively slow turnover of most enzymes and proteins, which can remain active in cells for hours or days after they have been synthesized. Consequently, it means that the beneficial (or toxic) effects of a gene-active hormone usually decrease slowly when administration of the hormone is stopped. 

O C, relatively stable to storage when frozen, remains active for at least 1 year [17]... 

In addition to the very large role that enzymes play in life processes and medicine and in industrial fermentation and related processes, enzymes are finding a growing role in industrial products, such as detergents, where enzymes tend to break down proteins to water-soluble proteoses nr peptones. Enzymes for such use must remain active at relatively high pH values (8.5 to 9.5) and remain stable for a long product shelf life. See also Detergents. 

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