Acetyl-L-methionine amide

The interaction of four cellular nucleophiles with the putative ultimate carcinogens N-sulfonoxy-2-[ring-3H]acetylaminofluorene (N-sulfonoxy-2-AAF) and N-acetoxy-2-[ring-3H] acetylaminofluorene (N-acetoxy-2-AAF), and with N-hydroxy-2-[ring-3H]acetylaminofluorene (N-hydroxy-2-AAF) activated to the ultimate carcinogens by enzymatic sulfonation or transacetylation was determined. The adducts were isolated and adduct formation was quantified by isotope dilution. The order of nucleophilicity of the acceptors was guanosine greater than tRNA congruent to polyguanylic acid (poly G) greater than N-acetyl-L-methionine when N-sulfonoxy-2-AAF, N-acetoxy-2-AAF or N-hydroxy-2-AAF activated by transacetylation were the electrophiles. In the case of N-hydroxy-2-AAF activated by enzymatic sulfonation, the order of nucleophilicity was N-acetyl-L-methionine greater than guanosine congruent to tRNA greater than poly G. The increase in the reactivity of N-acetyl-L-methionine is hypothesized to be due to cytosolic enzyme(s) which facilitate transfer of the methionine residue from the nitrogen to carbon atoms 3 and 1 of the fluorene moiety. Of the two synthetic esters, N-sulfonoxy-2- AAF exhibited greater electrophilicity than N-acetoxy-2-AAF. The rate of adduct formation of N-sulfonoxy-2-AAF and of N-acetoxy-2-AAF with each nucleophile was a function of nucleophile concentration, indicative of a bimolecular reaction mechanism. The interaction is thought to involve attack of the nucleophile on the uncharged ultimate carcinogen, although interaction with an ion pair cannot be eliminated. The mutagenicity of N-sulfonoxy-2-AAF, N-acetoxy-2-AAF and of enzymatically activated N-hydroxy-2-AAF was evaluated by the Ames test. N-Sulfonoxy-2-AAF was virtually inactive, while N-acetoxy-2-AAF exhibited weak mutagenicity. N-Hydroxy-2-AAF activated by enzymatic sulfonation exhibited greater mutagenicity than synthetic N-sulfonoxy-2-AAF. The mutagenicity and reactivity of ultimate carcinogens derived from N-hydroxy-2-AAF by enzymatic activation do not necessarily coincide with the mutagenicity and reactivity of the synthetic ultimate carcinogens.

The objective of current study was to investigate the effect of N-acetyl-l-methionine (NALM) supplementation on lactation performance and plasma variables in mid-lactating dairy cows. Forty-eight multiparous cows were blocked into 12 groups based on parity, days in milk, and milk production and were randomly assigned to 1 of the 4 treatments: 0, 15, 30, or 60 g/d of NALM per cow to supplement the basal diet. The experiment was conducted over a 13-wk period, with the first week as adaptation. The yields of milk, fat-corrected milk, and milk lactose were increased quadratically, and energy-corrected milk yield tended to increase with increased NALM supplementation in a quadratic manner. The dry matter intake, milk protein yield, milk fat yield, contents of milk composition (protein, fat, lactose, total solids, and milk urea nitrogen), feed efficiency, and body weight change were not affected by NALM supplementation. In addition, plasma methionine concentration was increased quadratically, and proline, total nonessential AA, and total AA concentrations were significantly higher in the 30 g/d group compared with that of the control group. However, other AA and total essential AA concentrations were not affected with supplementation of NALM. Adding NALM increased concentrations of total protein and globulin in plasma, but decreased plasma urea nitrogen concentration in a quadratic manner. Meanwhile, plasma malonaldehyde concentration decreased linearly as doses of NALM addition increased. Our results suggested that the supplementation of NALM improved milk yield and protein synthesis in the liver, and lowered lipid peroxidation in mid-lactating dairy cows.

A novel aminoacylase was purified to homogeneity from culture broth of Streptomyces mobaraensis, as evidenced by SDS-polyacrylamide gel electrophoresis (PAGE). The enzyme was a monomer with an approximate molecular mass of 100 kDa. The purified enzyme was inhibited by the presence of 1,10-phenanthroline and activated by the addition of Co2+. It was stable at temperatures of up to 60 degrees C for 1 h at pH 7.2. It showed broad substrate specificity to N-acetylated L-amino acids. It catalyzed the hydrolysis of the amide bonds of various N-acetylated L-amino acids, except for Nepsilon-acetyl-L-lysine and N-acetyl-L-proline. Hydrolysis of N-acetyl-L-methionine and N-acetyl-L-histidine followed Michaelis-Menten kinetics with K(m) values of 1.3+/-0.1 mM and 2.7+/-0.1 mM respectively. The enzyme also catalyzed the deacetylation of 7-aminocephalosporanic acid (7-ACA) and cephalosporin C. Moreover, feruloylamino acids and L-lysine derivatives of ferulic acid derivatives were synthesized in an aqueous buffer using the enzyme.