Nonheme Proteins

Iron constituent of cytochromes and other heme or nonheme proteins cofactor for a number of enzymes. 

Metal bound 02 stoichiometry (ligands) Fe 02 (heme, histidine) Fe 02 (heme, histidine) 2 Fe 02 (nonheme, protein side chains) 2 Cu 02 (nonheme, protein side chains)... 

Ferredoxin 11 1-2 1 -0.42 Nonheme protein with two Fe and two S accepts electrons from Photosystem I by way of intermediates soluble in aqueous solutions... 

There is a large body of knowledge on the coordination chemistry of iron-sulfur complexes and iron clusters particularly directed at the modeling and nnderstanding of the action of nonheme proteins whose active sites contain iron-sulfur units. These topics are discussed in detail elsewhere in this Encyclopedia here, the emphasis is on the basic coordination chemistry. 

Fig. 27. Electron flow in green plant photosynthesis. Vertical wavy arrows represent excitation of chlorophyll molecules by absorbed light. Reaction intermediates are as follows Z , unknown intermediate donating electrons to photocenter II Q , unknown intermediate accepting electrons from excited chlorophyll PQ, plasto-quinone, structurally similar to coenzyme Q or ubiquinone of Fig. 4 bss>, haa,, cytochrome components PC, plastocyanin, a copper-containing nonheme protein FR8, unknown ferredoxin reducing substance FD, ferredoxin FP, flavoprotein mediating reduction of NADP. ...

Hemocyanins (Hcl are oxygen-transport nonheme proteins I MW 10 lO ) which are found in the blood of some insects, crustaceans, and other invertebrates. One of the smallest He (MW 450,000) e.xiracted from spiny lobster Panulirus inierrupius consists of six subunits each containing two Cu atoms. Upon oxygenation, the deoxy form (Cu(I), colorless) turns to blue (Cu(ll), blue blood ) by binding one O2 molecule per two Cu atoms. 

Kuznetsov studied Brdicka catalytic waves for several nonheme proteins and proposed that complete unfolding accompanied adsorption of these biological molecules. Cytochrome c gave rise to weak Brdicka currents, probably as a consequence of having only three hidden sulfur atoms per molecule. Senda et have recently stated that cytochrome c Brdicka... 

Wilson (1967) has reported on the use of low temperatures (— 196 C) to sharpen the absorption bands of some nonheme iron proteins, e.g., ferredoxins of spinach and of Clostridium acidi-urici, and an adrenal protein. All three of these nonheme proteins have absorption maxima near 700 nm which disappear on reduction by dithionite. The oxidized spinach ferredoxin has two additional absorptions, a shoulder near 830 nm and a weak maximum at 930 nm. Wilson (1967) investigated the possibility that the absorbance of these bands, particularly the 714 nm band of spinach ferre-doxin, is sensitive to protein conformational changes in a manner analogous to the 695 nm band of ferricytochrome c (Schejter and George, 1964). 

Colneleic and colnelenic acids are degraded by oxidative cleavage of the ether to form aldehydic fragments. The. degradation is catalyzed by an enzyme in potato tubers but also occurs in the presence of Fe " ions and some nonheme proteins, e.g., ferredoxin. 

Recently, many nonheme metalloproteins which do not involve porphyrins as prosthetic groups have been discovered and provided a lot of new concepts on the O2 activation and substrate oxygenations [9]. However, the characterization of the nonheme proteins is much more difficult than that of the heme-proteins, because there are a variety of coordination structures of metal ions in the nonheme proteins [10]. In addition, some of the nonheme proteins show poor spectral features. In this chapter, biochemical studies on the nonheme metalloproteins acting as monooxygenases are reviewed. 

Weinberg JB, GiUceson GS, Mason RP, Chamulitrat W. 1998. Nitrosylation of blood hemoglobin and renal nonheme proteins in autoimmune MRL-lpr/lpr mice. Free Radic Biol Med 2A 1)-.191-196. 

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