Methionine bound

The second and third classes of selenoproteins form in a similar manner selenomethionine bound to the transfer ribonucleic acid (tRNA) for methionine competes with methionine bound to the tRNA for... 

Methionine bound to tRNA " can be formylated, but methionine bonded to tRNA cannot be. 

Fe in haem is bound in a mostly a-helical protein usually by histidine but sometimes by methionine, cysteine or tyrosine. Several such proteins are to be found in membranes. 

Methionine synthase deficiency (cobalamin-E disease) produces homocystinuria without methylmalonic aciduria. This enzyme mediates the transfer of a methyl group from methyltetrahydrofolate to homocysteine to yield methionine (Fig. 40-4 reaction 4). A cobalamin group bound to the enzyme is converted to methylcobalamin prior to formation of methionine. 

Sulfur-bound L-Met, as opposed to S,N-chelated L-Met, is more reactive as a ligand on Pt(II) and can be slowly replaced by N7 of G (95, 96). Transfer of Pt onto DNA via Met-containing peptides or proteins may therefore be possible. Monofunctional adducts of the type [Pt(en)(G)(L-Met-S)] appear to be very stable (97) and so methionine may play a role in trapping these adducts. Also, the high trans influence of S as a Pt(II) ligand can lead to the facile labilization of trans-am(m)ine ligands and this allows cisplatin to react with GMP faster in the presence of L-Met then in its absence (98), which introduces another route to DNA platination. 

The methyltransferases represent a relatively large number of enzymes that utilize the cofactor, S-adenosyl-L-methionine, in which the methyl group is bound to a positively charged sulfur, to transfer a methyl group to an oxygen, sulfur, or nitrogen atom in an appropriate substrate as shown in Figure 7.9 (8). 

Fe3+ also shows a strong affinity for the oxygen donor atoms of carboxylates as well as the phenoxide of tyrosine. Like cysteine, the sulfur ligand of methionine is often found bound to iron, for example in electron-transfer haemoproteins such as cytochrome c. 

Fig. 13. Stereo drawing of one contour level in the electron density map at 2 A resolution for the residue 54-68 helix in staphylococcal nuclease. Carbonyl groups point up, in the C-terminal direction of the chain the asterisk denotes a solvent peak bound to a carbonyl oxygen in the last turn. Side chains on the left (including a phenylalanine and a methionine) are in the hydrophobic interior, while those on the right (including an ordered lysine) are exposed to solvent.

The pyridinium chlorochromate (PCC) oxidations of pentaamine cobalt(III)-bound and unbound mandelic and lactic acids have been studied and found to proceed at similar rates.Free-energy relationships in the oxidation of aromatic anils by PCC have been studied. Solvent effects in the oxidation of methionine by PCC and pyridinium bromochromate (PBC) have been investigated the reaction leads to the formation of the corresponding sulfoxide and mechanisms have been proposed. The major product of the acid-catalysed oxidation of a range of diols by PBC is the hydroxyaldehyde. The reaction is first order with respect to the diol and exhibits a substantial primary kinetic isotope effect. Proposed acid-dependent and acid-independent mechanisms involve the rapid formation of a chromate ester in a pre-equilibrium step, followed by rate-determining hydride ion transfer via a cyclic intermediate. PBC oxidation of thio acids has been studied. ... 

Histone-lysine methyltransferases are chromatin-bound enzymes that catalyses the addition of methyl groups onto lysine or arginine residues of chromatin-bound H3 and H4 [151]. The methyl group is transferred enzymatically to the histone with S-adenosyl methionine as the methyl donor. Histone methylases have been isolated from HeLa S-3 cells [182], chick embryo nuclei [183], and rat brain chromatin [184]. The histone methyltransferases methylated H3 and H4 in nucleosomes [184]. Histone-lysine methyltransferase is a chromatin-bound enzyme [129,151]. Initial characterization of the Tetrahymena macronuclear H3 methyltransferase suggests that the enzyme has a molecular mass of 400 kDa. The enzyme preferred free histones rather than nucleosomes as substrate [138]. More recent studies have now... 

PRMTl, a nuclear receptor coactivator, exists as in a 330 kDa complex and is a H4 Arg-3 methyltransferase [133,215]. The enzyme appears to be a chromatin bound, and evidence from immunodepletion and knockout studies suggest that it is the principle, if not sole, H4 Arg-3 methyltransferase [133,215]. Mutation of the S-adenosyl methionine binding site in PRMTl annihilated its nuclear receptor coactivator activity with the androgen receptor, providing evidence for the importance of the methylation event in gene expression [215]. Yeast Rmtl, which is homologous to human PRMTl, methylates Arg-3 only in free H4 [208]. 

As with any metalloprotein, the chemical and physical properties of the metal ion in cytochromes are determined by the both the primary and secondary coordination spheres (58-60). The primary coordination sphere has two components, the heme macrocycle and the axial ligands, which directly affect the bound metal ion. The pyrrole nitrogen donors of the heme macrocycle that are influenced by the substitutents on the heme periphery establish the base heme properties. These properties are directly modulated by the number and type of axial ligands derived from the protein amino acids. Typical heme proteins utilize histidine, methionine, tyrosinate, and cysteinate ligands to affect five or six coordination at the metal center. 

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