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CNDO/2 calculations are reported for dilithium and disodium porphyrin. The total energy is calculated as a function of the metal-ring distance for symmetrical (D4h) structures. For dilithium porphyrin, the equilibrium metal-ring distance is 0.87 A and the metal-metal vibrational frequency is 123 cm-1. For disodium porphyrin, the distance is 1.64 A and the frequency is 77 cm -1. Little mixing of metal and porphyrin orbitals takes place; the two lowest unoccupied and the two highest occupied MOs hardly differ from those in porphyrin, but lower MOs are considerably rearranged.
Porphyrins c have been obtained from Rhodospirillum rubrum cytochrome c2, yeast cytochrome c, and horse heart cytochrome c and compared using proton magnetic resonance and circular dichroism. Identity of the spectra establishes that chemically and stereochemically the three porphyrins c are identical. Since the stereochemistry of the porphyrin alpha-thioether linkage is not affected in the conversion to porphyrin c, the stereochemistry at the porphyrin alpha-thioether bonds among the corresponding cytochromes c also must be the same. Differences between the proton magnetic resonance of R. rubrum cytochrome c2 and horse heart cytochrome c which were rationalized by invoking an opposite stereochemistry at these condensation sites (Smith, G. M., and Kamen, M. D. (1974), Proc. Natl. Acad. Sci. U.S.A. 71, 4303) must therefore be attributed to other factors.
Semi-empirical CNDO/2 MO calculations are reported for the ground states of porphyrin, 2,4-divinylporphyrin (DVP), and alpha, beta, gamma, delta-tetraphenylporphyrin (TPP). Results for TPP refer to the conformation with all phenyl groups perpendicular to the porphyrin ring, calculated to be 108 kJ mol-1 more stable than the coplanar conformation. The substituents withdraw electron density where they are attached to the porphyrin ring, increasing selected orbital energies. The vinyl groups also modify the electron population at nitrogen. CNDO/S calculations with extensive configuration interaction are reported for excited states. The lowest singlet states are closely similar in energy and composition for all three molecules, except for an extra state and more complex compositions in DVP above 3 eV. The lowest triplet states of porphyrin and DVP are very similar, while those of TPP are comparable in energy or composition but not both. Experimental data on the excited states are broadly consistent with the calculations, although comparisons for the excited triplets are tentative.
Thin layer chromatographic techniques for the separation and subsequent quantification of free porphyrins, coproporphyrin isomers and the methyl esters of porphyrins are described including a 2-dimensional system. The relevant RFs for a wide range of porphyrins are given. These methods have been in use in Cardiff and Barcelona for a number of years and were used in the survey of cases described by Pinol et al. (1975) which resulted in the discovery of the new porphyria, hepato-erythrocytic porphyria.
Porphyrin biosynthesis from exogenous ALA and PBG was observed over a period of from 1 to 8 hours in hemolysates of red blood cells from patients with AIP, PCT, and EPP. In all these conditions all porphyrins in the biosynthetic pathway through to PROTO were formed, with URO as the dominant component. Compared to normals, total porphyrin synthesis was lowered during the entire incubation period in both AIP and EPP, but enhanced in PCT. In hemolysates after 1 hour the second component of the pattern in AIP is COPRO, in PCT HEPTA and in EPP PROTO. Of the isomers, COPRO III predominates in all conditions (greater than 80%), whereas URO contains more isomer I than III. In intact red cells from controls, AIP, and PCT, COPRO is always the main component formed from ALA. Total synthesis is diminished in AIP by about 50%, in analogy to the findings on hemolysates from AIP. In heated hemolysates URO formation is diminished by half in AIP, but nearly double control values in PTC. In this sense URO'gen-I-synthase activity is increased in PCT. These findings reflect the underlying enzymatic defect: Diminished URO'gen-I-synthase activity in AIP, diminished URO'gen decarboxylase activity in PCT, and diminished activity of ferrochelatase in EPP.
1. Hydrated electrons, produced by pulse radiolysis react with porphyrin cytochrome c with a bimolecular rate constant of 3-10(10) M-1 S-1 at 21 degrees C and pH 7.4. 2. After the reduction step an absorbance change with a half-life of 5 microns is observed with the spectral range of 430-470 nm. A relatively stable intermediate then decays with a half-life of 15 s. 3. The spectrum of the intermediate observed 50 microns after the generation of hydrated electrons shows a broad absorption band between 600 and 700 nm and a peak at 408 nm. The spectrum is attributed to the protonated form of an initially produced porphyrin anion radical. 4. Reduced porphyrin cytochrome c reacts with ferricytochrome c with a bimolecular constant of 2-10(5) M-1- S-1 in 2 mM phosphate pH 7.4, at 21 degrees C and of 2 - 10(6) M-1-S-1 under the same conditions but at 1 M ionic strength. It is proposed that electron transfer in an analogous exchange reaction between ferrocytochrome c and ferricytochrome c occurs via the exposed part of the haem.
In 20 iron deficient patients and 21 normal controls the activity of the enzyme delta-ALA dehydratase of erythrocytes was assayed. In addition the urine porphyrins and porphyrin precursor excretions were measured. It was found that in sideropenic patients the erythrocyte delta-ALA dehydratase activity was almost constantly higher than in normals; the difference of the mean values being statistically significant (p less than 0.005). A significant diminution of delta-ALA (p less than 0.0025) urine excretion was observed, whereas the urine excretion of PBG, CP and UP was found within the normal limits. The results are compared to those reported by other authors.
The relationship between urinary excretion of porphyrins, porphyrin precursors and total oestrogens in normal pregnancy was investigated. Significant increases in total oestrogen, delta-aminolaevulinic acid (ALA) and coproporphyrin (COPRO) excretion were noted. However, no close correlation was found between total oestrogen excretion and urinary output of ALA and COPRO. The results suggest that the observed increases in ALA and COPRO excretion during pregnancy may not simply be the result of steroid-mediated induction of hepatic haem biosynthesis, as has been proposed.
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