Transportation, methyl groups

In acetate-catabohzing methanogens, enzyme-bound methylcorrinoids are also indicated to serve as intermediates in methyl-group transport. There, methane and carbon dioxide are formed from acetic acid (via acetyl coenzyme A, whose acetyl group is spht into carbon monoxide and a corrin-bound methyl group). Accordingly, the methyl-group... 

The effect of the substituents on chain mobility and chain packing has been related to the gas transport properties [209]. Role of symmetry of methyl group placement on bisphenol rings in PES shows the permeability coefficients in the following order ... 

Coenzymes serve as recyclable shuttles—or group transfer reagents—that transport many substrates from their point of generation to their point of utilization. Association with the coenzyme also stabilizes substrates such as hydrogen atoms or hydride ions that are unstable in the aqueous environment of the cell. Other chemical moieties transported by coenzymes include methyl groups (folates), acyl groups (coenzyme A), and oligosaccharides (dolichol). 

Deoxyrihonucleotides are generally formed by reduction of ribonucleoside diphosphates. This involves a series of redox reactions in which NADP+ and FAD play a role (see Section 15.1.1), with a subsequent electron transport chain. DNA contains thymine rather than uracil, so thymidine triphosphate (dTTP) is a requirement. Methylation of dUMP to dTMP is a major route to thymine nucleotides, and is dependent upon N, A °-methylenetetrahydrofolate as the source of the methyl group (see Box 11.13). 

On the other hand, desmethyl-retro-hydroxamate ferrichrome 15, where the terminal methyl groups were replaced by hydrogen, showed no signihcant growth promotion activity toward Arthrobacter flavescence, and only one third of the iron(III) transport efficiency toward U. sphaerogena, which confirms the importance of the methyl groups... 

The values given in column 3 of Table IV were obtained from the data in column 2 ((2) and (6)]. A comparison of the results for 14 and 15 indicates that the introduction of methyl groups at sites 4 and 5 (see 12), leading to central chirality R at both carbon atoms, is the main cause of enantiomer selectivity. This is in agreement with the only slightly different enantiomer selectivity of 16 relative to 15. As expected, the effect of 17 is reversed by 18. Although valinomycin 1 is chiral, no enantiomer selectivity was detectable (see Table IV). The potentiometrically determined enantiomer selectivity AEMF is correlated to the transport selectivity [(2), (6), (10), and (11)]... 

Water-soluble calix[ ]arenes (62 n = 4, 6, and 8) containing trimethylammonio-methyl groups act as efficient inverse phase-transfer catalysts in the nucleophilic substitution reactions of alkyl and arylalkyl halides with nucleophiles in water.126 (Inverse phase-transfer catalysts facilitate reactions between two immiscible reactants via the transport of an organic substrate into an aqueous solution of a second substrate, in which reactions take place.)... 

The structure-activity relationship is also demonstrated by an alternative experiment. Since the sedative property of a drug requires that the drug be transported directly to the nervous system, a decrease in hydrophobic bonding should result in an increase in sedative activity. The successive introduction of methyl groups to adamantane carboxamide (110) does result in a progressive increase in the sedative activity of the drug in mice 249 ... 

This sequence of reactions is incompletely understood but involves numerous oxidations of carbon groups, for example, the conversion of methyl groups to carboxylic acids, followed by decarboxylation. The end product, cholesterol, is the precursor to cholesterol esters in the liver and is transported to the peripheral tissues where it is a precursor to membranes (all cells), bile salts (liver), steroid hormones (adrenals and reproductive tissues), and vitamin D (skin, then liver, and finally kidney). 

An example of geometric isomerism is provided by the dimethylpyrrolidinecarboxanilides (18). Only when the methyl groups substituted on the pyrrolidine ring are in the ois-conformation is electron transport inhibited and phytotoxicity produced. The trans-isomer neither inhibits the Hill reaction, nor is it phytotoxic. 

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