Methionine reaction with

Proteins can be cleaved specifically at the amide bond on the carboxyl side of methionine residues by reaction with cyanogen bromide. BrC=N. 

Adenosine triphosphate, coupled reactions and. 1128-1129 function of, 157, 1127-1128 reaction with glucose, 1129 structure of, 157, 1044 S-Adenosylmethionine, from methionine, 669 function of, 382-383 stereochemistry of, 315 structure of, 1045 Adipic acid, structure of, 753 ADP, sec Adenosine diphosphate Adrenaline, biosynthesis of, 382-383 molecular model of, 323 slructure of, 24... 

Methionine. Methionine reacts with ATP forming 5-adenosylmethionine, active methionine (Figure 30-17). Subsequent reactions form propionyl-CoA (Figure 30-18) and ultimately succinyl-CoA (see Figure 19-2). 

Besada [12] described a spectrophotometric method for determination of penicillamine by reaction with nitrite and Co(II). Penicillamine is first treated with 1 M NaN02 (to convert the amino-group into a hydroxy-group), then with 0.1 M CoCl2, and finally the absorbance of the brownish-yellow complex obtained is measured at 250 nm. The process is carried out in 50% aqueous ethanol, and the pH is adjusted to 5.4— 6.5 for maximum absorbance. The calibration graph is linear over the concentration range of 0.25-2.5 mg per 50 mL, and the mean recovery (n = 3) of added drug is 99.7%. Cystine, cysteine, methionine, and other amino adds do not interfere. 

The N-terminal methionine residue of protein can also be employed for selective PEGylation using aldehyde-terminated PEG via a reductive amination reaction, because the N-terminal primary amine has a lower pAa of 7.8 than other amines such as lysines, whose pZa is 10.1 [7]. After reaction with aldehyde-terminated PEG at low pH, the resultant imine is reduced with sodium cyanoborohydrate to provide PEGylated protein (Fig. 4) [8, 9]. This technique was used for the production of Neulasta, which was approved for use by the FDA in 2002 [10]. 

Fig. 4 PEGylation at the N-terminal methionine residue. The difference in pKa. between the N-terminal amine and other amines in the protein enables site-specific PEGylation. After reaction with aldehyde-terminated PEG at low pH, reduction of the resultant imine produces PEGylated protein...

In contrast to the reactivity of N-sulfonyloxy and N-acetoxy esters of arylamides and arylamines, the relative reactivity of protonated N-hydroxy arylamines with nucleophiles generally decreases in the order DNA > denatured DNA > rRNA = protein > tRNA nucleotides s nucleosides s methionine = GSH (2,13-17,30,36,40,127,129, 130). Furthermore, the rate of reaction with DNA was found to be not only first order with respect to N-hydroxy arylamine concentration, but also first order with respect to DNA concentration (127,129,131). These data suggested that the reaction mechanism was... 

The low reactivity of both Cyt111 and Cyt11 toward NO can be attributed to occupation of the heme iron axial coordination sites by an imidazole nitrogen and by a methionine sulfur of the protein (28). Thus, unlike other heme proteins where one axial site is empty or occupied by H20, formation of the nitrosyl complex not only involves ligand displacement but also significant protein conformational changes which inhibit the reaction with NO. However, the protein does not always inhibit reactivity given that Cat and nNOS are more reactive toward NO than is the model complex Fem(TPPS)(H20)2 (Table II). Conversely, the koS values... 

Bromolactamization (11, 76). This reaction can be used for stereoselective preparation of 3,4-disubstituted 3-lactams.1 Thus the P,-y-unsaturated hydroxamic acid 1, prepared in several steps from tiglic acid, on reaction with bromine and K2C03 in aqueous CH,CN cyclizes mainly to a rrans-p-lactam (2). In contrast, the protected a-amino-p,y-unsaturated hydroxamic acid 3, prepared in several steps from L-methionine, cyclizes on reaction with bromine mainly to a ris-p-lactam (4). 

Direct evidence of the reaction of PAN with sulfhydryl compounds has since been obtained (PAN at 115 ppm for 1-10 min). - In the reaction with glutathione, the major products are oxidized glutathione (disulfide) and 5-acetylglutathione. Other sulfhydryl compounds (e.g., coenzyme A, lipoic acid, and cysteine) yield only oxidation products, with no evidence of 5-acetylation. However, acetylation reactions have been observed with alcohols and amines. Sulfur compounds other than thiols can undergo oxidation by PAN methionine is converted to methionine sulfoxide, and oxidized lipoic acid (disulfide) is converted to sulfoxide. 

Orotic acid in the diet (usually at a concentration of 1 per cent) can induce a deficiency of adenine and pyridine nucleotides in rat liver (but not in mouse or chick liver). The consequence is to inhibit secretion of lipoprotein into the blood, followed by the depression of plasma lipids, then in the accumulation of triglycerides and cholesterol in the liver (fatty liver) [141 — 161], This effect is not prevented by folic acid, vitamin B12, choline, methionine or inositol [141, 144], but can be prevented or rapidly reversed by the addition of a small amount of adenine to the diets [146, 147, 149, 152, 162]. The action of orotic acid can also be inhibited by calcium lactate in combination with lactose [163]. It was originally believed that the adenine deficiency produced by orotic acid was caused by an inhibition of the reaction of PRPP with glutamine in the de novo purine synthesis, since large amounts of PRPP are utilized for the conversion of orotic acid to uridine-5 -phosphate. However, incorporation studies of glycine-1- C in livers of orotic acid-fed rats revealed that the inhibition is caused rather by a depletion of the PRPP available for reaction with glutamine than by an effect on the condensation itself [160]. 

Distinct changes in several properties of lysozyme occur after reaction with ozone. The lytic activity of the ozonized lysozyme shows the same trend at various pHs as the native enz3mie (Fig. 2) this may suggest that the pK values of the ionizable groups involved in catalysis have not been altered by ozonplysis. The amino acid composition of ozonized lysozyme differs from that of the native enz3mie in three residues — methionine, tryptophan and t3H osine. None of the other amino acids is affected by ozone. The extensive loss of enz5miic activity must be ascribed to the oxidative modification of these three amino acid residues in the lysozyme. 

---