Methyl conjugated

The methyl transferases (MTs) catalyze the methyl conjugation of a number of small molecules, such as drugs, hormones, and neurotransmitters, but they are also responsible for the methylation of such macromolecules as proteins, RNA, and DNA. A representative reaction of this type is shown in Figure 4.1. Most of the MTs use S-adenosyl-L-methionine (SAM) as the methyl donor, and this compound is now being used as a dietary supplement for the treatment of various conditions. Methylations typically occur at oxygen, nitrogen, or sulfur atoms on a molecule. For example, catechol-O-methyltransferase (COMT) is responsible for the biotransformation of catecholamine neurotransmitters such as dopamine and norepinephrine. A-methylation is a well established pathway for the metabolism of neurotransmitters, such as conversion of norepinephrine to epinephrine and methylation of nicotinamide and histamine. Possibly the most clinically relevant example of MT activity involves 5-methylation by the enzyme thiopurine me thy Itransf erase (TPMT). Patients who are low or lacking in TPMT (i.e., are polymorphic) are at... 

With the exception of acetylation and methylation, conjugation renders the whole molecule more polar and hydrophilic (less lipid soluble). This facilitates excretion and reduces the likelihood of toxicity. 

Figure 20.4. Silver-ion impregnated HPLC chromatogram of methylated conjugated fatty acids of hydrogenated soybean oil. trans 13, trans 15-(peak 1), trans 12, trans 14-(peak 2), trans 11, trans 13-(peak 3), trans 10, trans 12-(peak 4), trans 9, trans 11-(peak 5), trans 8, trans 10-(peak 6), trans 7, trans 9-(peak l)ltrans 12, cis 14-(peak 8) cis 12, trans 14-(peak 9) trans 11, cis 13-(peak 10) cis 11, trans 13-(peak 11) cis 10, trans 12-/trans 10, cis 12-(peak 12) cis 9, transit-/trans 9, cis ll-(peak 13) trans 8, cis 10-/cis 8, trans 10-(peak 14), cis 10, c/sl2-(peak 15) cis 9, cis ll-(peak 16), cis 8, c/sl0-(peak 17). Source Jung and Jung, 2002.

O-methyl metabolite, with up to about 15% of the dose as unchanged drug after inhalation or oral administration, 68 to 94% of a dose is excreted as conjugated isoprenaline, with about 2 to 8% of a dose as the 3-0-methyl conjugate and less than 5% as unchanged drug or free 3-0-methylisoprenaline small amounts of a dose are excreted in the bile, mainly as metabolites. 

As is the case for other steroids, the Hver is the primary site for the inactivation of estrogens. The main biochemical reactions are hydroxylation, oxidation, reduction, and methylation. Conjugation with glucuronic or sulfuric acid, which imparts more water solubility to these steroids and thus allows them to be eliminated rapidly through the... 

S-carbonitrile, 4-amino-1-methyl-, conjugate monacid -4-carbonitrile, 5-amino-l-methyl-... 

Kolbe thus admitted the substitution of electronegative elements or groups in the radicals, at the same time retaining the electrochemical character of the substituents. The acetyl radical (see p. 355) is methyl conjugated with... 

Ion High-Performance Liquid Chromatographic Quantification of Free and Methylated Conjugated Linoleic Acids, lJ i 35 1147—1153 (2000). 

Spectra recorded in CDC1 Backbone methyl Terminal methyl Conjugated Unconjugated. 

Ostrowska, E., Dunshea, F.R., MuraUtharan, M., and Cross, R.F. (2000) Comparison of Silver-Ion High-Performance Liquid Chromatographic Quantification of Free and Methylated Conjugated Linoleic Adds, Lipids 35, 1147-1153. 

Methylation may occur on flavanols that contain ortho-hydroxy functional groups. The position of methylation of catechin and epicatechin has been identified as the 3 - in humans and several other species [30,48,51-55] although small amounts of 4 -0-methyl conjugates of catechin and epicatechin have been described in both human and rat urine [55,56]. 

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