Horse ferrocytochrome

Fig. 32. The high-frequency shifted portions, 9.15-12.5 ppm, of 400 MHz H NMR spectra of horse ferrocytochrome c in 90%H20/10% H20, pH 8.85, at 25 °C in the presence of the indicated concentrations of Gdn-HCl. (From ref. 123, 1997, with permission from the publisher.)...

Nitrosomas europaea cytochrome c oxidase purified from the bacterial cells cultured in a copper-deficient medium has 1 copper atom per 2 molecules of heme A. As the copper-deficient oxidase does not show g = 2.0 signal in EPR spectrum, it seems not to have Cua. However, the copper-deficient oxidase catalyze the oxidation of horse ferrocytochrome c at the same rate as the two- (or three)-copper containing oxidase does, though its activity to catalyze the oxidation of N. europaea ferrocytochrome c-552 is one third of that of the two- (or three)-copper oxidase (Numata et al., 1989). These results suggest that cytochrome c oxidase needs not necessarily Cua to catalyze the oxidation of ferrocytochrome c. Thus, from Rhodobacter sphaeroides, cytochrome cbb3 has been obtained, which does not have Cua and still shows cytochrome c oxidase activity (Garcia-Horsman et al., 1994). 

The ammonia-oxidizing bacteria biosynthesizes the cellular materials from carbon dioxide. For this purpose, they need NAD(P)H. Electrons to reduce NAD(P)+ seem to come from ferrocytochrome c-552 by the supply of energy, because Aleem (1966) reported that he had demonstrated that NAD(P)+ was anaerobically reduced with horse ferrocytochrome c on addition of ATP using the cell-free extracts of N. europaea, though the enzymatic system participating in the reduction of NAD(P)+ has not been known. However, every attempt by the author and his colleagues to reproduce his results has been unsuccessful to date. 

Gordon, S. L. and Wuethrich, K., Transient proton-proton Overhauser effects in horse ferrocytochrome c, J. Am. Chem. Soc. 100, 7094-7096 (1978). 

Recently, Sivakolundu and Mabrouk published an NMR solution structure of horse heart ferrocytochrome c in which the heme contains an Fe(II) ion. This solution structure was the first in which the cytochrome c protein was dissolved in a nonaqueous solvent a solvent mix of 70% water and 30% acetonitrile (ACN). The data obtained from the NMR study are deposited in the protein data bank (PDB) as (1) ILCl, the minimized average NMR structure and (2) 1LC2, the 30 lowest energy NMR structures. 

PROP Reduced form crystallizes as separate needles oxidized form as rosettes. Mol wt about 13,000. Cytochrome c2 Needles changing to squares. Mol wt about 13,000. Cytochrome c3 Needles. Mol wt 11,300. SYNS CROMOCI CYTOREST FERRICYTO-CHROME C FERROCYTOCHROME C HEMATIN-PROTEIN HORSE-CYTOCHROME C HORSE HEART CYTOCHROME C LANDRAX MYOHEMA-TIN NITROSYLFERRICYTOCHROME C... 

Fig 3. MCD spectra recorded at room temperature of low-spin ferric heme (ferricy-tochrome c, horse heart), high-spin ferric heme (metmyoglobin-HaO), low-spin ferrous heme (ferrocytochrome c), and high-spin ferrous heme (deoxymyoglobin). Intensities are indicated at the prominent peak and trough wavelengths in units of A/ cm T , where T = Tesla [taken from N. Foote, Ph.D. Thesis, UEA (1984)]. 

The enzyme contains two heme A molecules, two heme C molecules, one molybdenum atom, and five [Fe4S4] clusters in the molecule with molecular mass of 250 kDa. Molybdenum occurs as a complex with molybdopterin guanine dinucleotide (MGD) (Fukuoka et al 1987 Yoshino, 1994 Suzuki et al., 1997). The enzyme catalyzes the reduction of N. winogradskyi ferricytochrome c-550 and horse ferricytochrome c with nitrite, i.e it catalyzes the oxidation of nitrite with ferricytochromes c as the electron acceptor. The reaction is stimulated by Mn2+ and Ca2+. Although the enzyme catalyzes actively the oxidation of nitrite around pH 8, it shows also capability to catalyze the reduction of nitrate with ferrocytochrome c at pHs less than 6 the bacterium changes itself from a nitrifier to a denitrifieT at pHs less than 6. 

The structures of ferrocytochrome c from tuna (17) and bonito (23) are in essential agreement, and Fig. 9 of ref. 23 shows a stereo comparison of the heme and left channel aromatic ring orientations in these two molecules and in horse ferricytochrome. Because of the poor quality of the horse map, these latter orientations must be considered provisional, and in a sense this chapter is one year premature. A detailed comparison of accurate ring orientations in oxidized and reduced cytochrome will soon be possible, but cannot yet be made. Although the crystal forms obtained... 

Optimal activity of the purified enzyme solubilized in Triton X-100 is obtained in the presence of excess phospholipids. The pH optimum of the steady-state reaction with horse heart ferrocytochrome c occurs at pH 6, yielding a turnover of about 80 electrons/sec, similar to the value obtained for the enzyme from P. denitrificans. Remarkably, a purified membrane-bound c cytochrome, identified by its N-terminal sequence as cytochrome Ci from the 6c 1 complex, stimulates the rate of electron transfer between horse heart c5d ochrome c and the cytochrome c oxidase by about a factor of two. The in vitro enzyme assay with purified cytochrome oxidase and reduced amicyanin showed no activity only after the addition of endogenous cytochrome C550 (or horse heart cjfto-chrome c) did oxidation of amicyanin occur, in agreement with the sequence of electron transfer ami — cjft C550 CCO. 

A recent study by Rush et al. (157) indicates that inorganic complexes can serve as both structural and ET probes. Oxidation of horse heart ferrocytochrome c by [Co(bpy)3] and [Co(phen)3] at low ionic strengths (6-60 mM) was found to be independent of the concentration of the Co... 

A series of exciting papers on cytochrome c by Dickerson et al. includes a report on the structures at 2.8 A resolution of horse and bonito ferricyto-chromes, a speculative discussion on chain flexibility in ferricytochrome, a report of tuna ferrocytochrome at 2.45 A resolution, and a discussion of sequence and structure homologies in bacterial and mammalian-type cytochromes. ... 

Sutin s kinetic studies on the oxidation of horse-heart ferrocytochrome c by tris-(phen)cobalt(iii) have recently been extended to acid pH. The reaction is first-order with respect to each reactant but the dependence of the rate on [H+] is not simple. Measurements in chloride medium (7=0.13 mol 1 ) over the pH range 1—7 revealed a rate maximum at pH 2.9 (A =6.7x 10 1 mol" s at 25 °C). By contrast, the rate constants at pH 1.0 and 5.8 are 3.2 x 10 and 2.1 x 10 1 mol" S", respectively. Below pH 1.7, biphasic kinetics are observed, the slower reaction having a rate constant of ca. 2 s" (independent of oxidant concentration). The slow process is ascribed to a conformational change in the ferricytochrome c which is produced in... 

---