Prosthetic group, of enzymes

Molybdenum Milk, milk products dried legumes or pulses liver and kidney grains Prosthetic group of enzymes aldehyde oxidase Xanthine oxidase Electron transfer chain enzymes... 

Once the fungicides penetrate to the cell membrane or into the cytoplasm they may operate by devious means to disrupt vital functions. There is substantial evidence that the quinones immobilize the sultliydryl and imino prosthetic group of enzymes. The 8-hydroxyquinoline and dithiocarbamate compounds are active against copper and other metallic members of an enzyme system, presumably hy their ability to chelate metals. Heavy metals such as mercury alTect certain enzymes such as amylases and may serve as general protein precipitants. 

In enzymatic catalysis, the amazing unity of acid-base and redox mechanisms, in one of BRC H+ and e or H are transferred to prosthetic groups of enzymes, which results in redox transformations of the substrate. 

The answer is c. (Murray, pp 627—661. Scriver, pp 3897—3964. Sack, pp 121-138. Wilson, pp 287-320.1 In the Far East, rice is a staple of the diet. When rice is unsupplemented, beriberi can be manifest, since rice is low in vitamin Bi (thiamine). Thiamine pyrophosphate is the necessary prosthetic group of enzymes that transfers activated aldehyde units. Such enzymes... 

If the two wavelengths. A,- and Aj, and the two chromophores are very close, however, the denominator of these two terms, R and Rjt, becomes quite small and these terms can dominate in the summations for Rj and Rj. This has been demonstrated in a number of dinucleotide prosthetic groups of enzymes, such as flavin-adenine dinucleotide and nicotinamide-adenine dinucleotide. An example is given below for the adenine and nicotinate chromophores. 

From the standpoint of utilizing this effect it is fortunate that many coenzymes, prosthetic groups of enzymes, and substrates contain identifiable absorptions in the near ultraviolet as do the aromatic side chains of amino acids. Thus, if one could titrate a coenzyme or substrate onto an enzyme and note this type of reciprocal relations involving a transition in the enzyme, for example in a tryptophan or tyrosine group, and an absorption band in the group being added, then one would have identified an interaction at the active... 

Since co-enzymes and prosthetic groups of enzymes include a number of heterocyclic rings, it is possible that the alkaloids are related to them or associated with their formation. Alkaloids might also act as enzyme activators or inhibitors. 

One-electron reduction of oxygen can, in principle, occur by oxidation of any substance the redox potential of which is lower than or equal to -0.15 V (the redox potential of the 02/superoxide pair). Compounds with high kinetic barriers of reaction with O2 were selected by evolution. Highly reactive coenzymes and prosthetic groups of enzymes operating at the initial and middle steps of liie respiratory chain, such as coenzyme Q semiquinone (CoQH ) are exception of this rule. CoQH as an... 

Originally advanced as a tentative working hypothesis, the demonstration within the next few years that additional members of the vitamin B complex are prosthetic groups of enzymes, together with the apparent vindication of the thesis in the case of additional pharmacological agents (Green, 1946), led to a situation where the hypothesis assumed, in many circles, the transcendental quality of a natural law. 

Meat, meat products, offal and egg yolk are rich sources of vitamin Bg (Table 5.8). In foods of animal origin, the main compounds are pyridoxal and pyridoxamine, especially in the form of phosphate esters. For example, in meat the main form is present as pyridoxal 5 -phosphate (about two thirds of this vitamin are prosthetic groups of enzymes) bound to various proteins (such as imine), to a lesser extent as free pyridoxal 5 -phosphate, followed by pyridoxamine 5 -phosphate. In contrast, milk contains only about 10% of vitamin in bound forms. The vitamin content in milk and cheeses is relatively low. 

Prosthetic group is a generic term which comprises all groups bound to proteins including even those without any catalytic effect (cf. Chapt. IV-8). In this chapter we always refer to prosthetic groups of enzymes. 

Electrochemical communication between electrode-bound enzyme and an electrode was confirmed by such electrochemical characterizations as differential pulse voltammetxy. As shown in Fig. 11, reversible electron transfer of molecularly interfaced FDH was confirmed by differential pulse voltammetry. The electrochemical characteristics of the polypyrrole interfaced FDH electrode were compared with those of the FDH electrode. The important difference between the electrochemical activities of these two electrodes is as follows by the employment of a conductive PP interface, the redox potential of FDH shifted slightly as compared to the redox potential of PQQ, which prosthetic group of FDH and the electrode shuttling between the prosthetic group of FDH and the electrode through the PP interface. In addition, the anodic and cathodic peak shapes and peak currents of PP/FDH/Pt electrode were identical, which suggests reversibility of the electron transport process. 

A quite different approach came from Chance and others using heme enzymes (1947). Purified horseradish peroxidase has a characteristic absorption spectrum which was visibly altered in the presence of hydrogen peroxide. When an appropriate substrate was added it was oxidized by the hydrogen peroxide and the spectrum reverted to that of the original state of the enzyme. Similar studies were performed with catalase, showing that prosthetic groups in enzymes underwent reversible changes in the course of their reactions. 

At physiological pH, polyamines are fully protonated and polycationic. It is possible that the amino group of amines prevents SAM from reacting with ACS by interfering with the prosthetic groups of the enzyme. Polyamines such as putrescine, spermidine, and spermine, and methionine cycle intermediates such as MTA and KMB have been shown to have an inhibitory effect on ACS activity. ... 

The structure of cobalamin is more complex than that of folic acid (Figure 15.2 and 15.3). At its heart is a porphyrin ring containing the metal ion cobalt at its centre. In catalytic reactions the cobalt ion forms a bond with the one-carbon group, which is then transferred from one compound to another. Vitamin B12 is the prosthetic group of only two enzymes, methylmalonyl-CoAmutase and methionine synthase. The latter enzyme is particularly important, as it is essential for the synthesis of nucleotides which indicates the importance of vitamin B12 in maintenance of good health. 

Currently, Ni(I) macrocyclic complexes have attracted much attention. This is because Ni(II) tetraaza macrocyclic complexes catalyze the electrochemical reduction of C02 and alkyl halides, and it is proposed that the Ni(I) species are involved in such reactions (1,2, 76-79, 82, 124-126). Furthermore, F430, a Ni(II) hydrocorphinoid complex, is a prosthetic group of methyl coenzyme M reductase that catalyzes the reductive cleavage of S-methyl coenzyme M to methane in the final stage of C02 reduction to methane (127-130). An EPR signal detected in whole cells of Methanobacterium thermoautotrophicum has been attributed to an Ni(I) form of F430 in intact active enzyme (131,132). 

NAD(P)H is required in the bioreductions of many xenobiotic compounds. However, NADH or NADPH are not necessarily the entities that directly react with the organic substrate. Rather, the prosthetic groups of other enzymes are themselves reduced by NAD(P)H, and the resulting reduced enzyme components are the actual reactants involved in bond making and breaking of the xenobiotic substance. A prominent set of examples involves the flavin-dependent oxidoreductases. The key reactive portion in these flavoproteins is the three-ring flavin (FAD) which is reduced by NAD(P)H to FADH2 ... 

The pyruvate carboxylase reaction requires the vitamin biotin (Fig. 16-16), which is the prosthetic group of the enzyme. Biotin plays a key role in many carboxyla-tion reactions. It is a specialized carrier of one-carbon groups in their most oxidized form C02. (The transfer of one-carbon groups in more reduced forms is mediated by other cofactors, notably tetrahydrofolate and 5-adenosylmethionine, as described in Chapter 18.)... 

FIGURE 18-5 Pyridoxal phosphate, the prosthetic group of aminotransferases. (a) Pyridoxal phosphate (PLP) and its aminated form, pyri-doxamine phosphate, are the tightly bound coenzymes of aminotransferases. The functional groups are shaded, (b) Pyridoxal phosphate is bound to the enzyme through noncovalent interactions and a Schiff-base linkage to a Lys residue at the active site. The steps in the formation of a Schiff base from a primary amine and a carbonyl group... 

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