Enzyme activation specific activity

Hereditary deficiency of phosphoglycerate kinase (PGK) is associated with hereditary hemolytic anemia and often with central nervous system dysfunction and/or myopathy. The first case, reported by Kraus et al. (K24), is a heterozygous female, and the results are not so clear. The second family, reported by Valentine et al. (V3), is a large Chinese family, whose pedigree study indicates that PGK deficiency is compatible with X-linked inheritance. To date, 22 families have been reported (04, T25, Y3). Nine of these have manifested both symptoms five have shown only hemolysis seven have shown the central nervous system dysfunction and/or myopathy but without hemolysis and one case, PGK Munchen, is without clinical symptoms (F5). PGK II is an electrophoretic variant found in New Guinea populations (Y2). Red blood cell enzyme activity, specific activity, and the kinetic properties of this polymorphic variant are normal. 

International Unit (IU) Ratal (kat), the true SI unit of enzyme activity Specific activity that amount of enzyme protein which brings about the conversion of 1 (Imol of substrate to product per minute under stated conditions that amount of enzyme protein which brings about the conversion of 1 mole of substrate to product per second under stated conditions. enzyme activity (as IU or kat) per mg of total protein. This is a useful measure of the purity of an enzyme preparation... 

Prephenate aminotransferase The specific activity of this enzyme in Supernatant I was 19.2 nmol/min/mg, and the total activity was retained in Supernatant II following centrifugation at 60,000g. The homogenized pellet (about 300 mg of protein) exhibited enzyme activity (specific activity of... 

The specific enzyme to be used in an EIA is deterrnined according to a number of parameters including enzyme activity and stabiUty (before, during, and after conjugation), cost and availabiUty of the enzyme substrate, and the desired end point of the EIA, such as color. Most EIAs utilize a colored end point which can be readily deterrnined both visually and spectrophotometricaHy. Table 1 Hsts a number of enzymes which have been used in immunoassays and their substrates. 

Specificity for a particular charged substrate can be engineered into an enzyme by replacement of residues within the enzyme-active site to achieve electrostatic complementarity between the enzyme and substrate (75). Protein engineering, when coupled with detailed stmctural information, is a powerful technique that can be used to alter the catalytic activity of an enzyme in a predictable fashion. 

Chemical Pathology. Also referred to as clinical chemistry, this monitoring procedure involves the measurement of the concentration of certain materials in the blood, or of certain enzyme activities in semm or plasma. A variety of methods exist that allow (to variable degrees of specificity) the definition of a particular organ or tissue injury, the nature of the injurious process, and the severity of the effect (76). 

Specific enzyme activity Amount of substrate rendered into product per unit dry weight of enzyme protein per unit time. 

Nonrepetitive but well-defined structures of this type form many important features of enzyme active sites. In some cases, a particular arrangement of coil structure providing a specific type of functional site recurs in several functionally related proteins. The peptide loop that binds iron-sulfur clusters in both ferredoxin and high potential iron protein is one example. Another is the central loop portion of the E—F hand structure that binds a calcium ion in several calcium-binding proteins, including calmodulin, carp parvalbumin, troponin C, and the intestinal calcium-binding protein. This loop, shown in Figure 6.26, connects two short a-helices. The calcium ion nestles into the pocket formed by this structure. 

Glycogen synthase also exists in two distinct forms which can be interconverted by the action of specific enzymes active, dephosphorylated glycogen synthase I (glucose-6-P-independent) and less active phosphorylated glycogen synthase D (glucose-6-P-dependent). The nature of phosphorylation is more complex with glycogen synthase. As many as nine serine residues on the enzyme appear to be subject to phosphorylation, each site s phosphorylation having some effect on enzyme activity. 

The enzymatic transformation of natural products is by for file most attractive option. In this approach, it can be envisaged that sterols, which are relatively abundant, may be selectively modified to produce desired products. Hie diversity of enzyme activities, their reaction specificity, regiospecificity and stereospedfidty are all features which could contribute to carrying out the desired changes. This does not mean, however, that transformations using enzyme systems are simple. Nevertheless, biotransformations have become of vital importance in the production of steroids. 

Hen egg-white lysozyme catalyzes the hydrolysis of various oligosaccharides, especially those of bacterial cell walls. The elucidation of the X-ray structure of this enzyme by David Phillips and co-workers (Ref. 1) provided the first glimpse of the structure of an enzyme-active site. The determination of the structure of this enzyme with trisaccharide competitive inhibitors and biochemical studies led to a detailed model for lysozyme and its hexa N-acetyl glucoseamine (hexa-NAG) substrate (Fig. 6.1). These studies identified the C-O bond between the D and E residues of the substrate as the bond which is being specifically cleaved by the enzyme and located the residues Glu 37 and Asp 52 as the major catalytic residues. The initial structural studies led to various proposals of how catalysis might take place. Here we consider these proposals and show how to examine their validity by computer modeling approaches. 

Since endosulfan is a cytochrome P450-dependent monooxygenase inducer, the quantification of specific enzyme activities (e.g., aminopyrine-A -demethylase, aniline hydroxylase) may indicate that exposure to endosulfan has occurred (Agarwal et al. 1978). Because numerous chemicals and drugs found at hazardous waste sites and elsewhere also induce hepatic enzymes, these measurements are nonspecific and are not necessarily an indicator solely of endosulfan exposure. However, these enzyme levels can be useful indicators of exposure, together with the detection of endosulfan isomers or the sulfate metabolite in the tissues or excreta. 

The equilibrium particle diameter in the case of non agglomerate particle systems or the enzyme activity of immobilised enzymes after a certain exposure of time is entirely due to the reactor-specific comminution process, and conclusions can therefore be drawn regarding the maximum intensity of hydrodynamic stress. 

The diagram in Fig. 18 shows direct comparisons with the corresponding results for the floccular system. The particle diameters dpv and dp and the relative enzyme activity a/a in Fig. 18 show similar patterns of variation as with the specific impeller power P/V. It is therefore appropriate to represent these results by means of the correlation function obtained for the floccular system according to Eq. (20). As in Fig. 9, a clear correlation of the results is found for both systems (see Figs. 19 and 20). It is thus clear that particle disintegration in a stirred tank with baffles follows a similar pattern for other particle systems. 

The advantages of such biotransformation processes are (1) the relatively high yields which can be achieved with specific enzymes, (2) the formation of chiral compounds suitable for biopharmaceuticals, and (3) the relatively mild reaction conditions. Key issues in industrial-scale process development are achieving high product concentrations, yields and productivities by maintaining enzyme activity and stability under reaction conditions while reducing enzyme production costs. 

Despite the wide diversity of enzyme structures, most enzyme activity follows a general mechanism that has several reversible steps. In the first step, a reactant molecule known as a substrate (S) binds to a specific location on the enzyme (E), usually a groove or a pocket on the surface of the protein E + S ES The substrate binds to the active site through intermolecular interactions that usually include significant amounts of hydrogen bonding. 

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