Inactivation concentration

Figure 83 Plot of fcobs as a function of inactivator concentration for a single-step mechanism of inactivation.

Type of Antimicrobial Agent Inactivator Concentration Comment... 

The rate of enzyme inactivation is proportional to low inactivator concentration but is independent at high inactivator concentration [Eq. (1)]. 

Under conditions where it is not possible to approximate the steady state, i.e., constant inactivator concentration, it is possible to estimate /clnact and Kt, if the inactivator concentration and residual enzyme activity are quantified simultaneously. If a fixed quantity of enzyme and inactivator are combined under... 

To determine the Ki and kmact values, first a plot of the log of the enzyme activity versus time is constructed (Fig. 16a). The rate of inactivation is proportional to low concentrations of the inactivator, but becomes independent at high concentrations. In these cases, the inactivator reaches enzyme saturation (just as substrate saturation occurs during catalytic turnover). Once all of the enzyme molecules are in the E-I complex, the addition of more inactivator does not affect the rate of the inactivation reaction. The half-lives for inactivation (fi/2) at each inactivator concentration (lines a-e in Fig. 16a) are determined. The fi/2 at any inactivator concentration equals log 2/kina( t,appf in the limiting case of infinite inactivator concentration, fi/2 = 0.693/kiiiact (log 2 = 0.693). A replot of these half-lives versus the inverse of the inactivator concentration, referred to as a Kitz and Wilson replot, is constructed to obtain the K and kjuact values (Fig. 16b). 

Figure 16 (a) A plot showing time-dependent inactivation by affinity labeling agents and mechanism-based inactivators used for determination of kinetic constants, (b) Replot of the half-lives of inactivation from Fig. 16a versus the inverse of the inactivator concentration to determine the K and values for affinity labeling agents and mechanism-based inactivators. 

FIGURE 4.12 Kitz-Wilson plot of the half-lives (rate constants) for mechanism-based inactivation at each inactivator concentration. 

From this plot the half-lives (rate constants) for the inactivation by each concentration of inactivator can be calculated from the slopes of the individual lines. These half-life values are then plotted along the y-axis versus 1/[I] plotted along the x-axis. This plot is also known as a Kitz-Wilson plot (Fig. 4.12). In the case of a saturation reaction, (i.e., at infinite inactivator concentration there is a finite half-life) the point where the plotted line intersects the y-axis is equal to 0.693/kinact where A inact is the rate of inactivation and represents a complex mixture of 2 3 and 4 (see Scheme 4.5). The dissociation constant for the enzyme-mechanism-based inactivator complex (Ki) can also be estimated from this plot as the x-intercept of the line represents —l/Ki (Fig. 4.12). 

Fig. 1. An amplified outline scheme of the making of various wiaes, alternative products, by-products, and associated wastes (23). Ovals = raw materials, sources rectangles = wines hexagon = alternative products (decreasing wine yield) diamond = wastes. To avoid some complexities, eg, all the wine vinegar and all carbonic maceration are indicated as red. This is usual, but not necessarily tme. Similarly, malolactic fermentation is desired in some white wines. FW = finished wine and always involves clarification and stabilization, as in 8, 11, 12, 13, 14, 15, 33, 34, followed by 39, 41, 42. It may or may not include maturation (38) or botde age (40), as indicated for usual styles. Stillage and lees may be treated to recover potassium bitartrate as a by-product. Pomace may also yield red pigment, seed oil, seed tannin, and wine spidts as by-products. Sweet wines are the result of either arresting fermentation at an incomplete stage (by fortification, refrigeration, or other means of yeast inactivation) or addition of juice or concentrate.

Saponins dismpt red blood cells and may produce diarrhea and vomiting. They may also have a beneficial effect by complexing with cholesterol [57-88-5] and thus lowering semm cholesterol levels (24,25). In humans, intestinal microflora seem to either destroy saponins or inactivate them in small concentrations. 

The biochemical basis for the toxicity of mercury and mercury compounds results from its ability to form covalent bonds readily with sulfur. Prior to reaction with sulfur, however, the mercury must be metabolized to the divalent cation. When the sulfur is in the form of a sulfhydryl (— SH) group, divalent mercury replaces the hydrogen atom to form mercaptides, X—Hg— SR and Hg(SR)2, where X is an electronegative radical and R is protein (36). Sulfhydryl compounds are called mercaptans because of their ability to capture mercury. Even in low concentrations divalent mercury is capable of inactivating sulfhydryl enzymes and thus causes interference with cellular metaboHsm and function (31—34). Mercury also combines with other ligands of physiological importance such as phosphoryl, carboxyl, amide, and amine groups. It is unclear whether these latter interactions contribute to its toxicity (31,36). 

Metabolites of vitamin D, eg, cholecalciferol (CC), are essential in maintaining the appropriate blood level of Ca ". The active metabolite, 1,25-dihydroxycholecalciferol (1,25-DHCC), is synthesized in two steps. In the fiver, CC is hydroxylated to 25-hydroxycholecalciferol (25-HCC) which, in combination with a globulin carrier, is transported to the kidney where it is converted to 1,25-DHCC. This step, which requites 1-hydroxylase formation, induced by PTH, may be the controlling step in regulating Ca " concentration. The sites of action of 1,25-DHCC are the bones and the intestine. Formation of 1,25-DHCC is limited by an inactivation process, ie, conversion of 25-HCC to 24,25-DHCC, catalyzed by 24-hydroxylase. 

Pea.nuts, The proteins of peanuts are low in lysine, threonine, cystine plus methionine, and tryptophan when compared to the amino acid requirements for children but meet the requirements for adults (see Table 3). Peanut flour can be used to increase the nutritive value of cereals such as cornmeal but further improvement is noted by the addition of lysine (71). The trypsin inhibitor content of raw peanuts is about one-fifth that of raw soybeans, but this concentration is sufficient to cause hypertrophy (enlargement) of the pancreas in rats. The inhibitors of peanuts are largely inactivated by moist heat treatment (48). As for cottonseed, peanuts are prone to contamination by aflatoxin. FDA regulations limit aflatoxin levels of peanuts and meals to 100 ppb for breeding beef catde, breeding swine, or poultry 200 ppb for finishing swine 300 ppb for finishing beef catde 20 ppb for immature animals and dairy animals and 20 ppb for humans. 

In the presence of calcium, the primary contractile protein, myosin, is phosphorylated by the myosin light-chain kinase initiating the subsequent actin-activation of the myosin adenosine triphosphate activity and resulting in muscle contraction. Removal of calcium inactivates the kinase and allows the myosin light chain to dephosphorylate myosin which results in muscle relaxation. Therefore the general biochemical mechanism for the muscle contractile process is dependent on the avaUabUity of a sufficient intraceUular calcium concentration. 

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