Iron protein solubility

The functions of the heme is uncertain. The soluble mammalian succinate dehydrogenase resembles closely that of E. coli and contains three Fe-S centers binuclear SI of E° 0 V, and tetranuclear S2 and S3 of -0.25 to -0.40 and + 0.065 V, respectively. Center S3 appears to operate between the -2 and -1 states of Eq. 16-17 just as does the cluster in the Chromatium high potential iron protein. The function of the very low potential S2 is not certain, but the following sequence of electron transport involving SI and S3 and the bound ubiquinone QD-S66 has been proposed (Eq. 18-4). 

Aleman, V., S. T. Smith, K. V. Rajagopalan and P. Handler Soluble metallo-flavoproteins. In Non-Heme Iron Proteins Role in Energy Conversion, A San Pietro, ed. Antioch Press, Yellow Springs, Ohio, pp. 327—348 (1965). 

A wide range of soluble redox enzymes contain one or more intrinsic [2Fe-2S]2+ +, [3Fe-4S]+ , or [4Fe S]2+ + clusters that function in electron transport chains to transfer electrons to or from nonheme Fe, Moco/Wco, corrinoid, flavin, thiamine pyrophosphate (TPP), Fe S cluster containing, or NiFe active sites. Many have been structurally and spectroscopically characterized and only a few of the most recent examples of each type are summarized here. Dioxygenases that function in the dihydroxylation of aromatics such as benzene, toluene, benzoate, naphthalene, and phthalate contain a Rieske-type [2Fe-2S] + + cluster that serves as the immediate electron donor to the monomeric nonheme Fe active site see Iron Proteins with Mononuclear Active Sites). The xanthine oxidase family of molybdoenzymes see Molybdenum MPT-containing Enzymes) contain two [2Fe-2S] + + clusters that mediate electron transfer between the Moco active site and the Other soluble molybdoen-... 

Fig. 12.5. Biogenesis and assembly of cytochrome 6-c, complex in the inner mitochondrial membrane. Cytochrome fc-Cj complex contains at least five different subunits COREI (corl), COREII (corll), nonheme iron protein (Fe-S), cytochrome c, (cyt Cj), and cytochrome b (cyt b). Cytochrome f> is a mitochondrial gene product and is probably assembled into the inner membrane (IM) via vectorial translation by mitochondrial ribosomes. The other subunits are synthesized on cytoplasmic ribosomes as larger precursors. The precursors, perhaps in association with a cytoplasmic factor , are attached to receptors on the mitochondrial outer membrane (OM). The complex laterally diffuses to the junctions of the outer and inner membranes, and with the help of a hypothetical translocator the precursors are imported across the membrane. Pre-Corl, pre-Corll, and the pre-nonheme iron protein cross the two membranes, whereas cytochrome c, becomes anchored to the outer face of the inner membrane, facing the intermembrane space (IMS). Cytochrome b is assembled inside the inner membrane, and the nonheme iron protein and Corl and Corll are assembled into the matrix side of the inner membrane. The N-terminal extensions are removed by a soluble matrix protease. The N-terminal extension of cytochrome c, is removed in two steps the first is catalyzed by the matrix protease and the second probably by a protease located on the outer face of the inner membrane.

The presentation in 1993 of the structure of the hydroxylase component of methane monooxygenase (MMOH) by Rosenzweig et al. (15) is the third published three-dimensional structure of a diiron-oxygen protein (Fig. 1). The previous two are from hemerythrin (Hr) (16,17) and protein R2 of E. coli ribonucleotide reductase (RNR-R2) (18, 19). Some other dinuclear iron proteins with known fi-oxo or p.-hydroxo bridges are purple acid phosphatases (PAP) [(e.g., uteroferrin (Uf)] (20, 21), ferritins (in early stages of nucleation) (22), rubrerythrin (Rr) (23-26), nigerythrin (26), and soluble stearoyl-acyl carrier protein A desaturase (A-AGP) (27, 28). 

The oxygenation of the atmosphere increased the stability and hence the concentration of oxidized transition metal ions. Oxidation of Cu+ led to soluble Cu2+, whereas soluble Fe2+ was converted into Fe3+ which, in water, occurs mainly as Fe(OH)3, a poorly soluble compound. To maintain the function of vital iron proteins and enzymes, special accumulation and storage mechanisms had to be developed for iron [7 a, 7b],... 

While enzyme activity was partially restored easily by recombining the particles with the soluble components, the particles could be saturated with the soluble reducing system only when we realized that unexpectedly high concentrations of the non-heme iron protein were required. After the approximate saturation levels for NHI and Fp had been estimated, a set 6f assays was performed (Table II). 

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