Haeme

Chromoproteins. Compounds of proteins with haem or some similar pigments. 

Prepared by heating ammonium mucate, or from butyne-l,4-diol and ammonia in the presence of an alumina catalyst. The pyrrole molecule is aromatic in character. It is not basic and the imino-hydrogen atom can be replaced by potassium. Many pyrrole derivatives occur naturally, e.g. proline, indican, haem and chlorophyll. 

Infonuation about the haeme macrocycle modes is obtained by comparing the resonance Raman spectra of deoxyHb with HbCO. The d-d transitions of the metal are too weak to produce large enliancement, so the... 

Figure C3.1.10. (a) Steady state IR difference spectmm (dark minus light) of cytoclirome c oxidase CO complex measured at low temperature (127 K). This protein contains a copper atom situated immediately adjacent to a haem...

Magnetic circular dicliroism (MCD) is independent of, and thus complementary to, the natural CD associated with chirality of nuclear stmcture or solvation. Closely related to the Zeeman effect, MCD is most often associated with orbital and spin degeneracies in cliromophores. Chemical applications are thus typically found in systems where a chromophore of high symmetry is present metal complexes, poriihyrins and other aromatics, and haem proteins are... 

Perhaps the most important complex of iron(II) is heme (or haeme). Haemoglobin, the iron-containing constituent of the blood, consists essentially of a protein, globin, attached through a nitrogen atom at one coordination position of an octahedral complex of iron(II). Of the other five coordination positions, four (in a plane) are occupied by nitrogen atoms, each of which is part of an organic... 

Hgiiri IJ.4. Sdieimnic representation o] haem iparphin rinqs not shon n]... 

Cytochromes c (Cyt c) can be defined as electron- transfer proteins having one or several haem c groups, bound to the protein by one or, more commonly two, thioether bonds. Cyt c possesses a wide range of properties and function in a large number of different redox processes. 

Absorption spectra of standard solutions of Cyt c was obtained at different concentration. Maximum of absolution was observed at wavelength 410 nm. It is known haemoglobin and other haems have absolution maximum at the same wavelength. For elaboration of selective method of Cyt c determination in semm of mice its reaction with phtalocyanine of copper was investigated. Absorption maximum of Cyt c with Cu phtalocyanine in H SO was observed at wavelength 710 nm. Dependence on optical density at 710 nm against concentration of Cyt c have linear character in range 0.162-10-"-6.49-10 mol/L. 

Ancillary to the proteins performing these functions are others which transport and store the iron itself. All these proteins are conveniently categorized according to whether or not they contain haem, and the more important classes found in nature are listed in Table 25.7. 

The poisoning effect of molecules such as CO and PF3 (p. 495) arises simply from their ability to bond reversibly to haem in the same manner as O2, but much more strongly, so that oxygen transport is prevented. The cyanide ion CN can also displace O2 from oxyhaemoglobin but its very much greater toxicity at small concentrations stems not from this but from its interference with the action of cytochrome a. 

The oxygen-carrying function is performed in some invertebrates by haemerythrin which, in spite of its name, does not contain haem. It is a diiron-oxygen protein. See K. K. Anderson and A. Gralund, Adv. Inorg. Chem. 43, 359-408 (1995). 

Figure 25.9 Some non-haem iron proteins (a) rubredoxin in which the single Fe is coordinated, almost tetra-hedrally, to 4 cysteine-sulfurs, (b) plant ferredoxin, [Fe2S2(S-Cys)4], (c) [Fe4S4(S-Cys)4] cube of bacterial ferredoxins. (This is in fact distorted, the Fe4 and S4 making up the two interpenetrating tetrahedra, of which the latter is larger than the former).

Other non-haem proteins, distinct from the above iron-sulfur proteins are involved in the roles of iron transport and storage. Iron is absorbed as Fe" in the human duodenum and passes into the blood as the Fe protein, transferrin, The Fe is in a distorted octahedral environment consisting of 1 x N, 3x0 and a chelating carbonate ion which... 

The structure of the diamagnetic, cherry-red vitamin B12 is shown in Fig. 26.6 and it can be seen that the coordination sphere of the cobalt has many similarities with that of iron in haem (see Fig. 25.7). In both cases the metal is coordinated to 4 nitrogen atoms of an unsaturated macrocycle (in this case part of a corrin ring which is less symmetrical and not so unsaturated as the porphyrin in haem) with an imidazole nitrogen in the fifth position. A major... 

HKm-. hem-, haem-, -alaun, m. Micros.) hemalum (a hematoxylin-alum stain). 

Pemenna c nocTOHHHUM npo( )HAeM boahu. 106 5.2. IlocTOaHHue npO( iHAH, cOAepxaiUHe yAapHue boahu 111... 

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