Enzyme-containing complexes

The term for any enzyme-containing complex is composed of a numerator, which is the product of the concentrations of all ligands in the complex, and a denominator, which is the product of all dissociation constants between... 

The term for any enzyme-containing complex is composed of a numerator, which is the product of concentrations of all ligands in the complex and a denominator, which is the product of all dissociation constants between the complex and the free enzyme, i.e. [EA] = [A]/Ka, [El] = [I]/BQs, and [EAI] = ([A][I])/(KaKu). The subscripts is and ii denote slope effect and intercept effect respectively of the double reciprocal velocity plots. 

Understanding the mechanism of an enzyme requires the structural characterization of the various enzyme-containing complexes involved in the transformation... 

Kinetic data (steady-state and rapid reaction) can be used to identify the sequence of enzyme-containing complexes as substrates are converted to products, and to identify the rates of some or all of the elementary steps in the overall reaction. For instance, in a two-substrate reaction such as that catalyzed by lactate dehydrogenase (lactate+ NAD <- pyruvate+NADH), it can be shown that the... 

The three most common types of inhibitors in enzymatic reactions are competitive, non-competitive, and uncompetitive. Competitive inliibition occurs when tlie substrate and inhibitor have similar molecules that compete for the identical site on the enzyme. Non-competitive inhibition results in enzymes containing at least two different types of sites. The inhibitor attaches to only one type of site and the substrate only to the other. Uncompetitive inhibition occurs when the inhibitor deactivates the enzyme substrate complex. The effect of an inhibitor is determined by measuring the enzyme velocity at various... 

In this type of sequential reaction, all possible binary enzyme substrate complexes (AE, EB, QE, EP) are formed rapidly and reversibly when the enzyme is added to a reaction mixture containing A, B, P, and Q ... 

Although Zn2+ is essential to human nutrition, compounds of the two elements below zinc in the periodic table. Cd and Fig. are extremely toxic. This reflects the fact that Cd2+ and Flg2+, in contrast to Zn2+, form very stable complexes with ligands containing sulfur atoms. As a result, these two cations react with and thereby deactivate enzymes containing —SH groups. 

Beside coactivators so-called corepressors exist that are bound to transcription factors such as nuclear receptors and inhibit the initiation of transcription. These factors include the nuclear receptor corepressor (NCoR) and the silencing mediator of retinoic acid and thyroid hormone receptor (SMRT), which interact with nuclear receptors and serve as platforms for complexes containing histone deacetylases (HDACs). These enzymes cause the reversal of histone acetylation of histones leading to a tightening of chromatin and enhancing its inaccessibility for RNA polymerase containing complexes. 

Nickel exists in the tunicate Trididemnum solidum as the nickel complex of a modified chlorin (Bible et al. 1988) and is a component of a number of enzymes. Urease is the classic example of a nickel-containing enzyme, and several enzymes contain both nickel and iron. Details of enzymes that contain nickel have been provided in a review (Mulrooney and Hausinger 2003), and only brief summaries are provided ... 

Direct and indirect competition formats, illustrated in Figure 1, are widely used for both qualitative and quantitative immunoassays. Direct competition immunoassays employ wells, tubes, beads, or membranes (supports) on to which antibodies have been coated and in which proteins such as bovine semm albumin, fish gelatin, or powdered milk have blocked nonspecific binding sites. Solutions containing analyte (test solution) and an analyte-enzyme conjugate are added, and the analyte and antibody are allowed to compete for the antibody binding sites. The system is washed, and enzyme substrates that are converted to a chromophore or fluorophore by the enzyme-tracer complex are added. Subsequent color or fluorescence development is inversely proportionate to the analyte concentration in the test solution. For this assay format, the proper orientation of the coated antibody is important, and anti-host IgG or protein A or protein G has been utilized to orient the antibody. Immunoassays developed for commercial purposes generally employ direct competition formats because of their simplicity and short assay times. The price for simplicity and short assay time is more complex development needed for a satisfactory incorporation of the label into the antibody or analyte without loss of sensitivity. 

Activity-based protein profiling (ABPP) is a chemical proteomic strategy in which active-site-directed covalent probes are used to profile the functional states of enzymes in complex proteomes. Activity-based probes (ABPs) can distinguish active enzymes from their inactive zymogens or inhibitor-bound forms. They contain a reactive group intended to modify enzyme active sites covalently and a reporter group (typically rhodamine or biotin) that assists in detection and identification of protein targets. 

Fe-hydrogenase, which usually functions in the direction of hydrogen evolution, has been known for over 30 years. This enzyme contains a highly reactive complex Fe-S center in which one of the Fe atoms is complexed with CO and CN [5], The Fe hydrogenases have extremely high turnover numbers 6,000 s 1 for C. pasteuriamm and 9,000 s 1 for Desulfovibrio spp. Note that this is a thousand times faster than the turnover number of nitrogenase ... 

It should be added that MS-02 is not necessarily a mono-nuclear complex. It could be shown in a few cases that the catalytic activity of the metal ion is due to the formation of dinuclear metal-substrate complexes. Presumably in these species each oxygen atom of dioxygen coordinates to a different metal center. Such systems were extensively used to model the reactivity patterns of various enzymes containing a bimetallic active center. 

Xanthine oxidoreductase (XOR) is a molybdenum-containing complex homodimeric 300-kDa cytosolic enzyme. Each subunit contains a molybdopterin cofactor, two nonidentical iron-sulfur centers, and FAD (89). The enzyme has an important physiologic role in the oxidative metabolism of purines, e.g., it catalyzes the sequence of reactions that convert hypoxanthine to xanthine then to uric acid (Fig. 4.36). 

The closest organic specie to the inorganic boric acid are the boronic acids generally described as R-B(OH)2. Boronic acids have been shown to act as inhibitors of the subtilisins. X-ray crystallographic studies of phenylboronic acid and phenyl-ethyl-boronic acid adducts with Subtilisin Novo have shown that they contain a covalent bond between the oxygen atom of the catalytic serine of the enzyme and the inhibitor boron atom (Matthews et al, 1975 and Lindquist Terry, 1974). The boron atom is co-ordinated tetrahedrally in the enzyme inhibitor complex. It is likely that boric acid itself interacts with the active site of the subtilisins in the same manner. 

The values with tyrosinase are also given in the rate per Cu equivalent, considering that the enzyme contains 4 Cu ions (Mol. wt. 12,800) ( ). Much difference between the values with tyrosinase and those with other Cu complexes indicates that the rate of... 

EC 3.1.6.1) is a lysosomal enzyme that hydrolyzes sulfuric acid ester bonds. The enzyme exists in two forms, arylsulfatases A and B, that differ in substrate specificity and in sensitivity toward inhibitors [142][143]. Human tissues contain more arylsulfatase A than arylsulfatase B. The natural substrates of these enzymes are complex lipids such as cerebroside 3-sulfate, and gly-cosaminoglycans such as chondroitin 4-sulfate and derman sulfate [144], Deficiencies of these enzymes are associated with a number of lysosomal disorders. 

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