Myoglobin sulfoxidation

These techniques have been used successfully in the micro-Zdman degradation of the enzyme mouse sarcoma dihydrofolate reductase to obtain the amino acid sequence of the first 25 amino acids 455). Similarly, RPC has been used in coqjunction with the automated Edman technique for sequencing 32 residues of myoglobin 456). Methionine and its oxidation products, methionine sulfoxide and methionine sulfone, in methionine fortified foods have been analyzed as their dansyl derivatives 457). Lysine has been determined as its dansyl derivative in a study in which the stability of lysine in fortified wheat flour was evaluated (458). 

To increase the enantioselectivity of these myoglobin metalloenzymes, Lu and co-workers have successfully utilized a covalent linkage approach [62], In an earlier attempt a Mn(III)-salen complex was incorporated into apo-myoglobin by mutating residue 103 to cysteine, followed by modification with a methane thiosulfonate derivative of Mn(III)(salen) (Figure 5.16). This catalyst showed sulfoxidation activity however, the ee was only 12 %. As such a low ee might be a result of the ability of the bound ligand to exist in multiple conformations within the protein cavity, it was hypothesized that the rotational freedom of the salen complex could be limited if it was anchored at... 

Ozaki S, Matsui T, Watanabe Y (1997) Conversion of myoglobin into a peroxygenase a catalytic intermediate of sulfoxidation and epoxidation by the F43FI/H64L mutant. J Am Chem Soc 119 6666-6667... 

Pironti V, Nicolis S, Monzani E, Colonna S, Casella L (2004) Nitrite increases the enantios-electivity of sulfoxidation catalyzed by myoglobin derivatives in the presence of hydrogen peroxide. Tetrahedron 60 8153-8160... 

Methionine is very susceptible to oxidation and reacts with a variety of oxidants to give methionine sulfoxide (RS(00)CH3) or, in highly oxidative conditions, methionine sul-fone (RS(0)CH3) (Scheme 11.3). Whether methionine residues are susceptible to oxidation depends to a large extent on their exposure to the solvent, in proteins such as myoglobin and trypsin these residues are buried within the hydrophobic regions of the protein and are relatively inert under conditions of mild oxidation. in contrast, in proteins such as ribonucle-ase chymotrypsin, ° pepsin and... 

Dense gas antisolvent techniques are amenable to the precipitation of proteins because of the low solubility of these compounds in DGs such as carbon dioxide. Lysozyme, trypsin, myoglobin, and insulin are examples of peptides that have been precipitated from organic solutions using CO2 as an antisolvent. Both batch and semicontinuous DG antisolvent techniques have been used to precipitate proteins from organic solvents such as methanol, ethanol, and dimethyl sulfoxide. ... 

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