Properties of the Enzyme System

In the taurocholic acid synthesizing system of rat liver microsomes, the fact that the soluble cytoplasmic fraction could be substituted for, by CoA and ATP, appeared to indicate the existence of cholyl-CoA as an activated intermediate (12). This was independently observed by a number of investigators (13-17). In Bremer s studies (13), the conjugation of cholic acid with taurine by rat liver microsomes at pH 7.3-7.6 required coenzyme A, ATP, Mg2+, Mn +, and fluoride to inhibit ATPase activity. In some cases, cysteine and glutathione stimulated the activity. In this report, a reaction mechanism involving cholyl-S-CoA as an intermediate and AMP and pyrophosphate as reaction products was proposed, in which the transfer of the cholyl group from CoA to taurine and glycine is irreversible. Since hepatic microsomes 

In a similar investigation, using guinea pig liver microsomes, Elliott (18) demonstrated the formation of taurocholic acid when the microsomes were incubated in phosphate buffer in the presence of Mg +, CoA, ATP, potassium cholate, taurine, cysteine, and potassium fluoride. The complete incubation system consisted of 0.2 ml of 0.25 m phosphate buffer, pH 7.4 0.1 ml of 0.1 M MgS04 100 units of CoA 0.25 ml of 0.08 m ATP 0.1 ml of 0.04 m potassium cholate 0.1 ml of 0.1 m taurine 0.05 ml of 0.2 m cysteine 0.1 ml of 0.3 M potassium fluoride and 0.5 ml of microsomal suspension. 

Assay of Bile Acid Conjugating Activity in Human Liver Homogenates 

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Chen, I.W., and Charalampous, F.C., 1965, Biochemical studies on inositol. 8. Purification and properties of the enzyme system which converts glucose 6-phosphate to inositol. J. Biol. Chem. 240 3507-3512. 

Rl. Raina, A., and Hannonen, P., Biosynthesis of spermidine and spermine in regenerating rat liver Some properties of the enzyme systems involved. Acta Chem. Scand. 24, 3061 (1970). 

HISTIDINE decarboxylase INHIBITORS - The subject of histamine has regained considerable interest among chemists and biologists as evidenced by several recent reviews. 2, 83 of special relevance is the biosynthetic step via histidine decarboxylase, the enzyme decarboxylating 1-histidine to form histamine. Shepherd and Mackay wrote an excellent review of this topic in 1967 therefore, no attempt will be made here to discuss the properties of the enzyme system. 

The hydrogenase may be electrically wired with different semiconductors, metals and conducting materials as an electrode. This property of the enzyme is successfully used in design of different biomolecular device for renewable energy production and conversion systems based on molecular hydrogen as intermediate energy carrier. In many cases... 

The other constant in the equation, is often used to compare enzymes. is the substrate concentration required to produce half the maximum velocity. Under certain conditions, is a measure of the affinity of the enzyme for its substrate. When comparing two eu2ymes, the one with the higher has a lower affinity for its substrate. The value is an intrinsic property of the enzyme-substrate system and cannot be altered by changing [S] or [E]. 

In this section, enzymes in the EC 2.4. class are presented that catalyze valuable and interesting reactions in the field of polymer chemistry. The Enzyme Commission (EC) classification scheme organizes enzymes according to their biochemical function in living systems. Enzymes can, however, also catalyze the reverse reaction, which is very often used in biocatalytic synthesis. Therefore, newer classification systems were developed based on the three-dimensional structure and function of the enzyme, the property of the enzyme, the biotransformation the enzyme catalyzes etc. [88-93]. The Carbohydrate-Active enZYmes Database (CAZy), which is currently the best database/classification system for carbohydrate-active enzymes uses an amino-acid-sequence-based classification and would classify some of the enzymes presented in the following as hydrolases rather than transferases (e.g. branching enzyme, sucrases, and amylomaltase) [91]. Nevertheless, we present these enzymes here because they are transferases according to the EC classification. 

Metallic nanoparticles and single-walled carbon nanotubes (SWCNTs) exhibit nanoscale dimensions comparable with the dimensions of redox proteins. This enables the construction of NP-enzyme or SWCNT-enzyme hybrids that combine the unique conductivity features of the nanoelements with the biocatalytic redox properties of the enzymes, to yield wired bioelectrocatalyts with large electrode surface areas. Indeed, substantial advances in nanobiotechnology were achieved by the integration of redox enzymes with nanoelements and the use of the hybrid systems in different bioelectronic devices.35... 

From this point on there are numerous ways of proceeding with the analysis. Crude extracts can be made from different mutant cells. The extract from one mutant can be used to complement the extract from another mutant in tryptophan synthesis, which can lead to an assay for a particular enzyme carried by one mutant that is missing in the other mutant. The goal at this juncture is to purify each enzyme of the pathway so that the properties of the enzymes and the reactions they catalyze can be individually scrutinized. All of the tryptophan enzymes have been isolated from E. coli. Studies of other systems indicate a remarkable similarity for the operation of this pathway in different microorganisms and plants. 

The choice of reactor configuration depends on the properties of the reaction system. For example, bioconversions for which the homogeneous catalyst distribution is particularly important are optimally performed in a reactor with the biocatalyst compartmentalized by the membrane in the reaction vessel. The membrane is used to retain large components, such as the enzyme and the substrate while allowing small molecules (e.g., the reaction product) to pass through. For more labile molecules, immobilization may increase the thermal, pH and storage stability of biocatalysts. 

A diverse cross section of enzymes has been studied in Jerusalem artichoke (Table 10.8), some simply because the tuber provides a convenient source that can be easily stored. In other instances, especially where there are relatively unique properties involved, the focus has been on the role of the enzyme system in the species. The following describes several such enzymes. 

During the 1950s and 1960s, studies focussed on the milk lipase system, the mechanism of its activation and the physico-chemical properties of the enzyme(s) involved. From these studies it was concluded that more than one lipase was present and several attempts to purify a milk lipase were reported. Jensen (1964) reviewed much of this work. 

Bioenergetics provides a quantitative description of the transformation of materials and energy in living systems. Most biochemical reactions occur in pathways, in which other reactions continuously add substrates and remove products. The rate of reactions depends on the properties of the enzymes (large proteins produced in cells) that catalyze the reaction. Substrates bind at the active sites of enzymes, where they are converted to products and later released. Enzymes are highly specific for given substrates and products. Inhibitors of enzymes decrease the rate of reaction. 

The dimanganese systems constitute one of the unusual cases in which the data for the relatively sophisticated model complexes contrast with the rather sparse information available for most of the enzyme active sites. The properties of the synthetic systems are being used in a predictive fashion to assign structures to the enzymes as spectropic data are obtained. 

Studies with one-enzyme systems on a laboratory scale with the aim of small scale production or verification of the desired concept do not require a detailed kinetic analysis. The properties of the enzyme and of the reaction system should be investigated to choose convenient assay and reaction conditions (e. g. temperature, pH value, substrate and cosubstrate concentrations). Typically some essential enzyme data are provided by the enzyme supplier or can be taken from handbooks [41]. 

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