Methionine sulfur

Reaction of the binuclear complex [(bpy)Pd(p-OH)2Pd(bpy)]2+ with dl-methionine (met) obeys a simple second-order rate law (Aif = 46kJmol-1 AS = —101J K-1 mol-1). The mechanism suggested is rate-determining associative attack of the methionine-sulfur to give... 

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... 

The Type 1 copper ions are normally coordinated by three strong ligands, a cysteine and two histidines, and often have one or two weaker ligands such as methionine sulfur or oxygen. Type 3 coppers are usually each coordinated by three histidines, with a bridging ligand such as oxygen or hydroxyl anion. 

In this case also, the Cu(II) ion is coordinated to two histidine nitrogen atoms, a cysteine sulfur atom and a methionine sulfur atom with a distorted tetrahedral geometry. Since this protein has an overall positive charge (p/ = 10.6), it gives a well formed response for the Cu(II)/Cu(I) reduction ( ,o =+0.32 V vs. NHE) simply using a glassy carbon... 

Almost all of the sulfur needed for healthy bodies is found in amino acids as cysteine and methionine. Sulfur serves several important roles including as a cross-linking agent similar to that served by sulfur in the cross-linking, or vulcanization, of rubber. This cross-linking allows the various chains, which are connected by these cross-links, to remember where they are relative to one another. This cross-linking allows natural macromolecules to retain critical shapes to perform necessary roles. 

Additional information has been obtained from single crystal, polarized optical and ESR spectroscopic studies924 on poplar plastocyanin, which have allowed a correlation of the electronic structure of the blue copper active site with its geometric structure. In summary, the three dominant absorption bands at 13 350, 16 490 and 17 870 cm-1 were assigned to CysS- Cu (d 2-,2 charge-transfer transitions. The methionine makes only a small contribution, due to the long Cu—S(Met) bond (2.9 A) and the poor overlap of the methionine sulfur orbitals with the dx y orbital of copper. Histidine-Cu charge transfer contributes to the weaker absorptions at 21 390 and... 

Rauk A, Armstrong DA, Fairlie DP (2000) Is oxidative damage by (1-amyloid and prion peptides mediated by hydrogen atom transfer from glycine a-carbon to methionine sulfur within (1-sheets. J Am Chem Soc 122 9761-9767... 

Furthermore, based on earlier calculations (39) for the type 1 copper protein plastocyanin, ligand-field parameters for the blue copper in laccase have been derived. These reports (37,38) also include a structural representation of the type 1 center composed of a flattened tetrahedron (D2d symmetry) with two imidazole side-chains, a cysteine sulfur, and a fourth ligand (which probably is methionine sulfur), bound to the metal ion. Although no such low-temperature experiments have been performed with ascorbate oxidase, one might anticipate similar structural features for the blue type 1 centers. 

Fetal pig epidermis contains hyaluronic acid and chondroitin 4-sulfate containing mucopolysaccharide (S15) as does human epidermis (M13), and some of the enzymes of uronic acid metabolism are present in human epidermis (F24). Also Barker et al. (B6) have shown uptake of radioactive sulfate into epidermis, and Braun-Falco et al. (B33) have shown that psoriatic epidermis is more active than normal epidermis in accumulating radioactive sulfate in vitro. There is also a suggestion that methionine sulfur may be preferentially accumulated in psoriatic lesions (B26, L6). There seems to be little doubt, therefore, that mucopolysaccharides are formed, and there is some suggestion that they may be formed in greater amounts in psoriatic skin lesions. The next section will consider the possibility that they are of importance in the cell membrane and intercellular contact. 

The figures suggest that a considerable proportion of the sulfur may be present as methionine, the epidermis being comparable with fibrinogen where cystine and methionine are about equal in quantity (56). Though the measurements are as yet few it is probably very important to pay close attention to the relative quantities of cystine- and methionine-sulfur in different types of epidermis. 

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