Cytochrome lysine-modified

Reaction with Chemically Modified Cytochrome c. Chemically modified (CDNP) cytochrome c derivatives have been prepared by Margoliash and colleagues (22). Lysine residues react as in (17),... 

Second-order rate constants (25°C) for the oxidation of singly modified CDNP-Lysine Cytochrome c Derivatives by Co(phen)3 + (kCo), Fe(CN)63- (kFe) and PCu(II) (kCu) at... 

The copper metalloenzymes are involved in oxygen-using reactions. These enzymes include cytochrome c oxidase (respiratory chain), lysyl oxidase (collagen synthesis), and dopamine [3-hydroxylase (neurotransmitter synthesis). Lysyl oxidase is a small protein with a molecular weight of 32 kDa. This enzyme contains an unusual modification, namely cross-linking between two different parts of its polypeptide chain. The cross-linked region consists of a structure called lysine tyrosylquinone (Klinman, 1996). Two amino acids are involved in this cross-linked structure, and these are Lys 314 and Tyr 349. Lysine tyrosylquinone is used as a cofactor and is necessary for the catalytic activity of the enzyme. Other copper metalloenzymes contain a related cofactor, namely 2,4,5-tiihydrox5q5henylalanine (topaquinone, TPQ). Serum amino oxidase is a copper metalloenzyme that contains TPQ. TPQ consists of a modified residue of phenylalanine. The copper in the active site of the enzyme occurs immediately adjacent to the TPQ cofactor. 

Besides heme P-460 of hydroxylamine oxidoreductase, cytochrome P-460 has been isolated from N. europaea (Erickson and Hooper, 1972 Miller et al., 1984 Numata et al., 1990). Cytochrome P-460 shows a weak activity of hydroxylamine oxidoreductase, and its molecule is composed of 3 subunits of 18 kDa. As the amino acid sequence of the cytochrome differs from that of hydroxylamine oxidoreductase and DNA encoding the cytochrome is found to be different from that of the oxidoreductase, the cytochrome is not a proteolytic fragment of the oxidoreductase (Bergman and Hooper, 1994b). Indeed, cytochrome P-460 has recently been crystallized and its spatial structure has been determined (Pearson et al., 2007). Its heme is a modified heme C in which lysine residue links to... 

Many of the adsorbates used to modify metal electrodes produce self-assembled monolayers (SAMs), in which the terminal functional groups provide good binding sites for proteins. For example, cytochrome c, which is positively charged and contains an excess of lysine residues... 

Besides the permselective properties, the electrocatalytic properties of ECP films can be also used for the amperometric detection of some target molecules. Accordingly, electrodes modified with PPy, polythiophene (PTh), PAni, and their derivatives were found to catalyze the electrochemical oxidation of ascorbic acid [127-129], NADH [115, 116,130], dopamine [128], pyrrolo-quinoline quinone [131] as a coenzyme of some oxidoreductases, and quinone and derivatives [132, 133]. Selectivity exhibited by these materials could be enhanced by the introduction of an appropriate substituent onto the polymer backbone. So, a facilitated electron transfer between cytochrome c and carboxylic acid or carboxylate-substituted PPy [134] or polyindole [135] has been observed. As such an effect was not obtained with unsubstituted polymer films, the cytochrome c-polymer interaction was e lained on the basis of binding between the polymer substituents and the lysine residues on the redox protein. 

Results derived from the use of modified cytochrome c lysines indicate that the interaction of cytochrome c with cytochrome probably involves complementary charge interactions between positively charged lysine groups on cytochrome c and negatively charged carboxyl groups on cytochrome 5 (Salemme, 1976). The same modifications that effect cytochrome 5 activity also effect the cytochrome c oxidase activity toward cytochrome c (Ng et al, 1977). 

To study the formation of a complex between cytochromes a and c, chemically modified cytochrome c was used in experiments on the cytochrome oxidase activity in place of native cytochrome c. As is known well, about twenty lysine residues are present per molecule of cytochrome c. About 70% of these were acetylated with acetic anhydride (Section II.B.2.a). In other experiments, about 70% of these groups were succinylated with succinic anhydride (Section II.B.2.6). By these procedures, it is generally believed that the e-NHj group of lysine is substituted first, although there is some possibility that in the above treatment not only this group but also the other amino acid residues such as histidine are substituted. 

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