Hemochromogen

Fig. 4. Visible spectra of catalase, compound I, and compound II 5 [xM (heme) beef liver catalase (Boehringer-Mannheim) in 0.1 M potassium phosphate buffer pH 7.4, 30°C. Compound I was formed by addition of a slight excess of peroxoacetic acid. Compound II was formed from peroxoacetic acid compound I by addition of a small excess of potassium ferrocyanide. Absorbance values are converted to extinction coefficients using 120 mM for the coefficient at 405 nm for the ferric enzyme (confirmed by alkaline pyridine hemochromogen formation). Spectra are corrected to 100% from occupancies of f 90% compound I, 10% ferric enzyme (steady state compound I) and 88% compound II, 12% compound I (steady state compound II). The extinction coefficients for the 500 to 720 nm range have been multiplied by 10. Unpublished experiments (P.N., 1999).

Early attempts at preparing P-450 from membranes were thwarted by the loss of absorption in the 450 nm region (CO complex) and the appearance in its place of absorption at 420 nm (7, 2, 5, 7). The P-420 pigment preserves all the characteristics of a heme-protein and the only heme present is protoheme. The spectra of the P-420 complex are given in Table 1 as they provide a basis for the discussion of P-450. The P-420 spectra are in all respects those of normal hemochromogens i. e. simple six-coordinate Fe(II) and Fe(III) hemo-proteins such as cytochrome b. 

Figure 12. MCD spectra of the pyridine hemochromogens (ferrous bis-pyridine adducts) of alkaline-denatured Spirographis heme-reconstituted myoglobin (-----) and myeloperoxidase (-----) (both in A) and of iron oc-...

Figure 8. Absorption spectrum of ferriheme undecapeptide (—) and of ferroheme undecapeptide (hemochromogen) (- ) in 0.05 M sodium tetraborate, pH 9. The right-hand ordinate is for the Soret (y) band and for the absorbances at wavelengths shorter than 210 nm. The hemochromogen bands are labelled a-s. As there are no residues in the undecapeptide with chromophores absorbing at wavelengths greater than 240 nm, the 280 nm, e and S bands are clearly due to the heme chromophore. Reproduced, with permission, from [11],...

The same nitrogenous bases that react with heme also react similarly with hemin but have in general a much lower affinity. These compounds are called parahematins and with the corresponding hemochromogens form a well-known redox system. 

The potentials of these systems will be discussed later in connection with estimates of the ionization potential of the hemochromogen in aqueous solution. The effect of increasing alkalinity on these systems is somewhat complex for there is evidence in some cases that an equilibrium of the following type can occur. 

This behavior may be contrasted with that of the hemochromogens where there is no evidence for similar replacement reactions, but considerable oxidative attack on the porphyrin ring occurs giving compounds named by Lemberg, Cortis-Jones, and Norrie oxyporphyrin hemochrome and... 

Unfortunately there is not sufficient thermal data for direct calculation of I in the case of heme, hemochromogens, and reduced peroxidase. In the first three cases, however, estimates can be based on a knowledge of their oxidation-reduction potentials. 

It may be concluded from this discussion that heme, hemochromogens, and the hemoproteins could undergo similar free radical and electron transfer reaction as the free ferrous and ferric ions. On thermochemical grounds reactions (1), (3), and (4) should be very rapid and reactions (o) and (a) should be more rapid than with ferrous ion in contrast to reaction (i), the ferric form reacting with hydrogen peroxide which should proceed extremely slowly. 

Hematin a was prepared from purified cytochrome oxidase as described (29). The hematin solution was made by dissolving the dried samples in phosphate buffer containing 1% Emasol 1130. Its concentration was determined by the pyridine hemochromogen method in a mixture of 20% pyridine and 0.05N NaOH an extinction coefficient of 27.4 mM cm." at 589 m/x was used (29). 

Hemochromes (hemochromogens). Complex compounds of heme with bases such as primary amines, ammonia, pyridine, nicotine, imidazole, etc. when Fe(IIl) is the central atom instead of Fe(ll), the term is hemichromes or ferrihemochromes. 

Pauling, L. and C.D. Coryell Magnetic properties and structures of hemochromogens and related substances. Proc Nat Acad Sci USA 22 ... 

The magnetic properties and structure of the hemochromogens and related substances. Proc. Natl. Acad. Sci. 22 (1936) 159—163. (Linus Pauling and Charles D. Coryell). 

Microcrystallographic or microchemical techniques rely on the fact that certain derivatives of hemoglobin have the tendency to crystallize. It is possible to find either crystals of hematin or crystals of hemochromogen (depending on whether the hem molecule is degraded to an iron(II) or iron(III) pigment). 

Pig. 3. Derivatives of myoglobin of importance in meats. In the outer circle are represented the insoluble hemochromogens obtained by coagulation. Only in the case of the cured meat pigment is the denatured compound red. Dotted portions represent possible intermediates between metmyoglobin and the cured meat pigment. 

Barnes, R. H., Lundberg, W. 0., Hanson, H. T., and Burr, G. 0.1943. Effect of certain dietary ingredients on the keeping quality of body fat. J. Biol. Chem. 149, 313. Barron, E. S. G., and Lyman, C. M. 1938. Studies on biological oxidations. X. Oxidation of unsaturated fatty acids with blood hemin and hemochromogens as catalysts. J. Biol. Chem. 123, 229. 

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