Cysteine myoglobins

Mb Sperm whale myoglobin, an oxygen-binding protein 153 amino acid residues. Note that Mb lacks cysteine. 

Cytochromes were first named and classified on the basis of their absorption spectra (Figure 21.9), which depend upon the structure and environment of their heme groups. The b cytochromes contain iron—protoporphyrin IX (Figure 21.10), the same heme found in hemoglobin and myoglobin. The c cytochromes contain heme c, derived from iron-protoporphyrin IX by the covalent attachment of cysteine residues from the associated protein. UQ-cyt c... 

Heme coenzymes (8) with redox functions exist in the respiratory chain (see p. 140), in photosynthesis (see p. 128), and in monooxygenases and peroxidases (see p. 24). Heme-containing proteins with redox functions are also referred to as cytochromes. In cytochromes, in contrast to hemoglobin and myoglobin, the iron changes its valence (usually between +2 and +3). There are several classes of heme (a, b, and c), which have different types of substituent - Ri to - R 3. Hemoglobin, myoglobin, and the heme enzymes contain heme b. Two types of heme a are found in cytochrome c oxidase (see p. 132), while heme c mainly occurs in cytochrome c, where it is covalently bound with cysteine residues of the protein part via thioester bonds. 

Silver nitrate has been found to react with cysteine, as in hemoglobin,412 or more often with histidine, as in myoglobin, trypsin and carboxypeptidase A.414 In most cases the reaction was similar to that for Hg2+. 

Fading of acetone extracts of pure NO-myoglobin solutions could be prevented by adding 1 ml of fresh 0.5% neutralized cysteine hydrochloride to 9 ml of NO-myoglobin solution. 

Iron protoporphyrin IX (heme) is found in the b-type cytochromes and in hemoglobin and myoglobin. In heme c, cysteine residues of the protein (R) are attached covalently by thioether links to the two vinyl (—CH=CH2) groups of protoporphyrin IX. Heme c is found in the c cytochromes. In heme A, which is found in the a cytochromes, a 15-carbon isoprenoid side chain is attached to one of the vinyls, and a formyl group replaces one of the methyls. 

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... 

The cytochrome c oxidase protein is thought to consist of two heme iron centers (heme a with two axial histidines and heme 03 with one axial histidine (analogous to myoglobin)) and two copper centers (Cua with two histidine, two cysteine, and one water/tyrosine ligand in its oxidized state and Cub with three histidine, one methionine, and one H2O/HO" ligands). The CuA/heme a pair constitute two coupled, one-electron redox couples (low potential, 0.4V) that facilitate (a) electron transfer from cytochrome c(Fe ) at the matrix side of the inner mitochondrial membrane as well as (b) proton transfer from the mitochondrial matrix across the inner membrane to the cytosol. At the cytosol side of the inner mitochondrial membrane, the CuB/heme a- pair constitute the binding site for O2 as well as the conduit for its high-potential four-electron, four-proton reduction to two H2O molecules. 

Zager R and Burkhart K. Differential effects of glutathione and cysteine on Fe2-i-, Fe3-i-, H202 and myoglobin-induced proximal tubular cell attack. Kidney Int 53 1661-1672,1998. 

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