Inhibition of formation

Chaudhri and colleagues46 calculated the rate of reaction 31 assuming that the final product (CH3)2S is due only to reaction of H atoms. From the inhibition of formation of (CH3)2S by Fe(CN)63 - and from the known rate constant for H + Fe(CN)63 they found /c31 = 3.3 x 10 1 s They said that error associated with this value is probably high... 

The inhibition of formation of NPYR and NDMA in fried bacon by the use of cure-solubilized a-tocopherol (500 mg/kg) has been demonstrated by Fiddler et al. (50). Walters et al. (53) also reported reduced levels of N-nitrosamines in the vapors during the frying of bacon in fat containing a-tocopherol. It has also been shown that a-tocopherol is dispersed quite effectively during frying of bacon slices therefore, application to bacon may be made by spray or dip to overcome the problem of water insolubility (51). Controlled addition of this antioxidant may be an effective and practical way of reducing the concentration of N-nitrosamines in cooked... 

As safe nutrient ingredients in many food systems, as well as available from commercial synthesis, the combination of vitamins C and E represents very useful compounds for the nutritional inhibition of formation of tumorigenic N-nitroso compounds. 

These relations both demonstrate the inhibition of formation of the tetrahedral state which can be clearly attributed to steric crowding. Such a correlation as (5) confirms the attack at the neighbouring carbonyl group and this intramolecular catalysis for all this series. The activation parameters for the alkaline hydrolysis of these esters were also measured and are shown in Table 1. The enthalpies of activation of the 2-formyl, 2-acetyl, 2-propionyl, 2-isobutyryl and 2-pivaloyl esters are exceptionally small. These are... 

Kelly DP, Syrett PJ. 1964a. Inhibition of formation of adenosine triphosphate in... 

Jobb DB, Hunsinger R, Meresz O, Taguchi VY (1992) A study of the occurrence and inhibition of formation of N-nitrosodimethylamme (NDMA) in the Ohsweken water supply. In Proceedings of the fifth national conference on drinking water, Winnipeg, Manitoba, Canada... 

FTB = inhibition of formation of thromboxane B2 from [l-l4C]arachidonic acid [79,80] ... 

Results obtained from these studies revealed that, of all the lipoprotein fractions tested, the formation of insoluble complexes with pectin was limited specifically to LDL. The pH optimum of the observed interaction was found between pH 4.3 and 5.2. The interaction between pectin and LDL was found to be optimal in 0.05 M phosphate buffer, and increase in the molarity of buffer inhibited the formation of complexes. Furthermore, presence of divalent cations such as Mg, Ca and Mn in concentrations above 1 mM in the reaction mixture caused the inhibition of formation of complexes between pectin and LDL. 

One type of inhibition assay is based on the formation of a colored or fluorescent product from a chromogenic or fluorogenic substrate and inhibition of formation of color or fluorescence by antioxidants. A popular chromogenic substance used... 

Ethyleneimine enamines do not isomerize owing to the inhibition of formation of (110) as a result of the angle strain involved. A confirmation of this hypothesis is that the reaction of X,N,N, N -tetramethylguanidine with /3-chloroacrylonitrile gives the retained enamines (Fanshawe et al., 3... 

The hydrophobic ferrocene moiety should establish favorable van der Waals interactions with lipid structures involved at the interface with aqueous content of the DV, positioning FQ in the same catalytic site as hematin [157]. This preferential location of FQ should cause inhibition of formation of hemozoin more efficiently than CQ does. 

Most NSAIDs attenuate the antihypertensive effect of p-blockers (but not perhaps of atenolol), presumably due to inhibition of formation of renal vasodilator prostaglandins, leading to sodium retention. 

Some interesting simulations have been used to investigate crystallization and deposition processes, in order to obtain a fundamental understanding of how these processes can be inhibited. The inhibition of formation of waxes (mixtures of normal alkanes that form lamellar structures) was examined.302 Gas hydrate formation has been investigated, and it was demonstrated that inhibition of methane hydrate by a octomer of polyvinylpyrrolidone was able to be simulated,302 and simulations were used to assist in developing a new class of inhibitors of gas-hydrate formation.303... 

The effect of aloe polysaccharides on chemopreventive agent was examined on inhibition of formation of B[a]P-adducts DNA in vitro and in vivo 81, 82). Also, a mannose rich polysaccharide, PAC-1 isolated from aloe has shown to have potent stimulatory activity on murine peritoneal macrophage. When PAC-1 was administrated in vivo is capable of prolonging the siuvival of tumor bearing mice 83). 

The dihydrofolate reductase inhibitor, methotrexate (Fig. 8.47), was developed as an anticancer drug, whose inhibition of formation of folic acid coenzymes would block purine synthesis. In other words, it was designed to induce a folic acid deficiency. Notice in Figs. 8.50 and 8.51 that formation of dTMP, FGAR, and AICAR also causes the oxidation of tetra-hydrofolate to dihydrofolate. The latter must be reduced by dihydrofolate reductase to tet-rahydrofolate before active coenzyme can form again. Thus, not only does methotrexate inhibit the initial formation of the tetrahydro-folate moiety, it blocks regeneration of the coenzyme form. 

Acetazolamide and dorzolamide inhibit CA on both the luminal membrane and in the PCT cell. Inhibition of C02 formation in the lumen decreases its intracellular availability. This, together with inhibition of formation of carbonic acid (CA is reversible), decreases intracellular bicarbonate and H+ levels. 

The alkylation of aromatic compounds using alkyl halides and a Lewis acid only requires a small amount of catalyst. Because Lewis acids form complexes with carbonyl compounds, the Lewis acids are effectively removed from the reagent system to the extent that product is formed. Although an equilibrium exists between the product complex and free Lewis acid, there is an apparent inhibition of formation of the acylating species. The net effect is that the amount of the ketone that is formed is normally proportional to the molar quantity of catalyst added. In reactions using acyl halides, completion occurs when slightly more than 1 mol of catalyst is used. When using a carboxylic anhydride, an excess over 2 mol of catalyst will usually be required because the other product, a carboxylic acid, will also complex with the Lewis acid. 

Alanine appears to be formed primarily by alanine dehydrogenase in A. cylindrica, C. licheniformey P. boryanumy and A. nidulanSy because the inhibition of formation of glutamate and glutamine by methionine sulfoximine is not accompanied by a comparable inhibition in the formation of alanine (Table I). Moreover, alanine formation by these species was not reduced in the presence of aminooxy acetate, an inhibitor of amino transfer reactions (I3,J4). However, in A. variabilis alanine appears to be formed by a transamination reaction, because synthesis of [ N]alanine from was strongly inhibited in the presence of... 

The sequential labeling of first citrulline and then arginine are consistent with the idea that citrulline is a substrate for the synthesis of arginine. In cyanobacteria, citrulline appears to be formed by the condensation of carbamyl phosphate with ornithine (27). The inhibition of formation of citrulline (and arginine) by methionine sulfoximine, azaserine, and aminooxy acetate could be due to the reduced formations of ornithine from glutamate and carbamyl phosphate from glutamine. In... 

While inhibition of formation of biosynthetic precursors upstream of FPP is possible, the j>otential deleterious effects are great given the widespread use of FPP in other biological processes within cells. However, selective inhibition of FPTase should be feasible and has the added implied advantage of having more beneficial and fewer harmful downstream consequences. This rationale has been the major impetus for identifying specific inhibitors of FPTase and has been the focus of many pharmaceutical companies and academic institutions. 

Feedback repression is the inhibition of formation of one or more enzymes in a pathway by a derivative of the end product. In many (but not all) amino acid biosynthetic pathways, the amino add end product must first combine with its transfer RNA (tRNA) before it can cause repression. Feedback repression is a widespread regulatory device especially for the synthesis of molecules intended for incorporation into macromolecules, e.g. amino adds, purines, and pyrimidines. Synthesis of vitamins also appears to be controlled by feedback repression, as well as by catabolite regulation (Birnbaum et al, 1967 Sasaki, 1965 Newell and Tucker, 1966 Wilson and Pardee, 1962 Papiska and Lichstein, 1968). Regulation of vitamin synthesis is important since only a small number (probably about 1000) of vitamin molecules are required per cell whereas many molecules of an average amino acid (probably 50 million) are required. An extremely wasteful case of vitamin overproduction would develop if enzymes for vitamin synthesis were produced at the same rate and were as active as the amino acid biosynthetic enzymes. 

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