Proteins porphyrin-containing

The stereochemistry and functions of all iron porphyrin-containing proteins can be attributed to the varied electronic structure of iron for the oxidation and spin states that are stable in physiological environments. Theoretical descriptions of the electronic structure of iron should be, in principle, applicable to the understanding of structure-function relationships in hemeproteins. 

It is a beautiful red, iron-porphyrin-containing protein which functions as a link in the chain of the cell-respiration enzymes, the iron atom now taking up and now giving off an electron, and the iron thus alternating valency between the 3-valent ferri and the 2-valent ferro stages. It is a very pleasant substance to work with, not merely because it is lovely to look at, but also because it is uncommonly stable and durable. From 100 kg heart-meat of horse one can produce 3-4 g of pure cytochrome c. The molecule weighs about 12,000 and contains one mol iron porphyrin per mol. 

INTRODUCTION IRON-CONTAINING PROTEINS WITH PORPHYRIN LIGAND SYSTEMS... 

The preceding sections of Chapter 7 have discussed iron-containing proteins and enzymes having a porphyrin ring system. Section 7.9 presents a short introduction to the many non-heme iron-containing proteins and enzymes. Two of these are iron-sulfur proteins (Section 7.9.2) and iron-oxo proteins (Section 7.9.3). 

Ubiquinone is readily reduced to ubiquinol, a process requiring two protons and two electrons similarly, ubiquinol is readily oxidized back to ubiquinone. This redox process is important in oxidative phosphorylation, in that it links hydrogen transfer to electron transfer. The cytochromes are haem-containing proteins (see Box 11.4). As we have seen, haem is an iron-porphyrin complex. Alternate oxidation-reduction of the iron between Fe + (reduced form) and Fe + (oxidized form) in the various cytochromes is responsible for the latter part of the electron transport chain. The individual cytochromes vary structurally, and their classification... 

In free heme molecules (heme not bound to protein), reaction of oxygen at one of the two open coordination bonds of iron (perpendicular to the plane of the porphyrin molecule, above and below) can result in irreversible conversion of Fe2+ to Fes+. In heme-containing proteins, this reaction is prevented by sequestering of the heme deep within the protein structure where access to the two open coordination bonds is restricted. One of these two coordination bonds is occupied by a side-chain nitrogen of a His residue. The... 

The electron carriers that participate in the flow of electrons to 02 are a structurally diverse group. Occupying a central position are a series of heme-containing proteins, the cytochromes. Hemes are porphyrins with iron at the center (see chapter 10). Three main types of cytochromes, a, b, and c, exist and are distinguished by different substituents on the periphery of the porphyrin ring and different modes of attachment of the porphyrin to the protein (fig. 14.3). Cytochrome c is a small, water-soluble protein associated loosely with the inner mitochondrial membrane. Another c cytochrome (c,), two b cytochromes (bL and bH), and two a cytochromes (a and a3) are embedded in the membrane as parts of large complexes described below. 

Iron-containing proteins are classified as either heme proteins or nonheme iron proteins. The former contain iron that is coordinated to a porphyrin... 

G. N. La Mar, J. D. Satterlee and J. S. de Ropp, in The Porphyrin Handbook , eds. K. M. Kadish, K. M. Smith and R. Ruilard, Academic Press, New York, 2000,, Vol. 5, p. 185. A thorough account of NMR of heme-containing proteins including useful background information on heme electronic structure. 

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