A-Acetylmethionine

A/-2-Methyl-2-(o-phenylazophenoxy)propionyl, 562 A/-4-Chlorobutyryl, 563 A/-Acetoacetyl, 563 A/-3-(p-Hydroxyphenyl)propionyl, 563 (A/ -Dithiobenzyloxycarbonylamino)acetyl, 563 A/-Acetylmethionine Derivative. 563 4,5-Diphenyl-3-oxazolin-2-one, 564... 

This enzyme [EC 3.5.1.16], also known as acetylornithi-nase and A -acetylornithinase, catalyzes the reaction of water with A -acetylornithine to produce acetate and ornithine. The enzyme also catalyzes the hydrolysis of A -acetylmethionine. 

A-Acetylmethionine amide [CH3SCH2CH2CH(NHCOCH3)CONH2] gives the cation radical with the 3 c-bond between atoms S and O belonging to the amide function, but not between S and N. Specifically, one-electron oxidation of a methionine part in (3-amyloid peptide has been associated with the neurotoxicity of these sequences (Schoeneich et al. 2000). This peptide is the major constituents of senile plaques in Alzheimer decease. 

A -Acetylmethionine Derivative (Chart 9). Cleaved by alkylation of the thioether with iodoacetamide followed by cyclization. 

The oxidation of iodide by the following complexes has been studied [AuCU], [AuBr4] Ni(III) Cu(III) together with the redox reactions of I2 and (SCN)2 radical ions with tris(2,2 -bipyridine) complexes of Os(II) and Os(III). The oxidation by iodine of A -acetylmethionine methyl ester is catalyzed by carboxylic acid buffers, in a complicated reaction involving the formation of a carboxylic acid anhydride. ... 

D-methionine DL- acetylmethionine D -aminoacy lase A.lcaligenes denitrificans 208... 

Quench the oxidation by the addition to the peptide solution of at least a 4-fold molar excess of N-acetylmethionine or sodium sulfite over the concentration of periodate in the reaction mixture. Pre-dissolve the quencher in buffer at a higher concentration prior to adding an aliquot of it to the reaction solution. React for 10 minutes. 

Quench the reaction by immediate gel filtration on a desalting column. If a dextran-based resin is used for the chromatography, the support itself will react with sodium periodate to quench excess reagent. Alternatively, N-acetylmethionine may be added to quench the reaction, because the thioether of the methionine side chain will react with periodate to form sulfoxide or sulfone products (Geoghegan and Stroh, 1992). In addition, sodium... 

Comparative studies on amino acid sequences of 12 mammalian metallothioneins have been reported.1457 They are all similar and contain 61 residues JV-acetylmethionine and alanine are at the N and C termini, respectively. The cysteinyl residues are distributed fairly uniformly along the polypeptide chain with a predominance of —Cys—X—Cys— sequences. 

The opsin consists of protein (ca. 80-85% of which is rhodopsin), phospholipids and carbohydrates and contains very little cholesterol (1-3%) (for a review, see [6]). While the molecular weight (e.g., 40000 for bovine rhodopsin) [7], carbohydrate [8,9], lipid and amino acid [10-12] composition have been established for some rhodopsins, there is as yet no example of a visual pigment for which the full amino acid sequence is known. Only a quarter of about the 300 residues of rhodopsin have been sequenced [13,14], 39 residues at the N-terminus and 40 residues at the C-terminus. The structure of the moiety containing retinal, i.e., retinal-lysine-alanine, which is located in the carboxy-terminal region has, however, been elucidated ([15] see also [78] and references therein). The N-terminal residue was identified as acetylmethionine [16]. 

In neutral and slightly alkaline media, MPO-compound I can react directly with iodides, bromides, chlorides (K16), thiocyanates, Al-acetylmethionine, cysteine, pyridine nucleotides (S20), and phenols (K16), including tyrosine (H14) and thyroid hormones. Some of these reactions have certain biological importance. In extensive studies, Klebanoff el al. investigated the potential function of MPO as an iodide-oxidizing enzyme (K16). It was found that iodide is rapidly oxidized, forming a bactericidal derivative which produces a fall in the number of viable Escherichia coli 10 times more effectively than bromide and 100 times more effectively than chloride, if used as MPO substrates. Extremely low concentrations of iodides and bromides in leukocytes and blood plasma, however, seem to limit the importance of iodide oxidation in bacteria killing mechanisms. 

V-acetylmethionine in quantities equal to LZM. Inactivation of LZM also may be restricted upon addition of /V-acetylcystine or /V-acetyltryptophan. The /V-acetylo-tryptophan competes with LZM for the oxidizing agent. Amino compounds binding hypochlorite to relatively stable chloramines, such as leucine, lysine, and taurine, do not protect LZM from MPO-mediated reaction. Oxidation of tryptophan residues in lysozyme molecules treated with HOC1 occurs along with a decrease of lysozyme spectral properties at 280 nm. 

The effect of N-acetyl substitution in methionine on the nature of transients formed after one-electron oxidation was studied as a function of pH and NAM concentration. The observed absorption bands with X = 290 nm, 360 nm, and 490 nm were respectively assigned to a-(alkylthio)alkyl, hydroxysulfuranyl and dimeric radical cations with intermolecular three-electron bond between sulfur atoms. N-acetylmethionine amide (NAMA) (Chart 7) represents a simple chemical model for the methionine residue incorporated in a peptide. Pulse radiolysis studies coupled to time-resolved UV-Vis spectroscopy and conductivity detection of N-acetyl methionine amide delivered the first experimental evidence that a sulfur radical cation can associate with the oxygen of an amide function vide infra). ... 

In a neutral amide -C(=0)-NH2, the carbonyl oxygen atom represents the better nucleophile compared to nitrogen atom. This fact is corroborated by pulse radiolysis studies of N-acetylmethionine methyl ester (NAMME) (Chart 7) showing similar kinetic and spectral features to NAMA. The theoretical parameters calculated by DPT (including TD-DFT) methods support to a large extent the experimentally identified one-electron oxidation mechanism of NAMA. ... 

An example of an acylase to perform a resolution is provided by the Degussa process to L-methionine (1). The racemic acetylmethionine (2) is prepared by a chemical synthesis. The acylase hydrolyses only the L-isomer (Fig. 2). The D-isomer is racemized by base and put back into the process stream (48). 

The amino acid sequences of many mammalian metallothioneins are known." They all contain 61 residues with the cysteine residues distributed along the full length of the polypeptide chain, and with N-acetylmethionine and alanine at the N- and C-termini, respectively. All 20 cysteine residues are involved in the binding of up to seven metal ions via thiolate linkages. A typical amino acid sequence is shown in Figure 44. 

Complex forms of CRM 3 with (a) (R)- and (S)-Af-acetylmethionine methylester, and (b) (R)- and (S )-N-3,5-dinitrobenzoylleucine methyl-ester. White, light-gray, dark-gray, and black balls, represent hydrogen, carbon, nitrogen, and oxygen, respectively. 

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