PAPER CHROMATOGRAPHY OF IRON COMPLEXES OF PORPHYRINS

Effects of concurrent oral administration of lead, selenium or monensin on hepatic porphyrin levels in broiler chickens during sub-acute toxicosis

Liver-porphyrin levels were found to have increased during sub-acute lead toxicosis. The presence of selenium or monensin in the diet of lead-intoxicated birds resulted in a further increase of liver-porphyrin levels. The results of this study indicate the presence of an interaction between lead and selenium or monensin in producing an increase in porphyrins in the liver tissue of broiler chickens.

Heme is a positive regulator of cytochrome P-450 gene transcription

Inhibitors of heme biosynthesis such as CoCl2, 3-amino-1,2,4-triazole, and thioacetamide block the 3-methylcholanthrene-mediated induction of cytochrome P-450 (c + d) messenger RNAs and their transcription in rat liver. This effect is specific, since the messenger RNA levels for albumin and glutathione transferase (Ya + Yc) and their transcription are not significantly influenced under conditions of heme depletion. Exogenous administration of heme at very low doses (50 micrograms/100 g body wt) is able to completely counteract the effects of the heme biosynthetic inhibitors on cytochrome P-450 (c + d) messenger RNA levels and their transcription. This constitutes a direct proof for the role of heme as a positive regulator of cytochrome P-450 gene transcription.

Non-aqueous liquid chromatography of some metalloporphyrins on a reversed-phase column

The effect of the hetaerons tetraphenylarsonium chloride (Ph4AsCl) and tetraphenylarsonium perchlorate (Ph4AsClO4) on the retention of neutral and cationic metalloporphyrins on a reversed-phase column with an acetonitrile-tetrahydrofuran (85:15, v/v) mobile phase was investigated. The adsorption properties of the two hetaerons on the stationary phase were dramatically different. While Ph4AsCl adsorbed, reaching saturation at a concentration of 4 mM, Ph4AsClO4 did not adsorb. The retention of neutral metalloporphyrins was unaffected, while cationic metalloporphyrins demonstrated decreasing retention with an increase in the concentration of either hetaeron. The possible equilibria involved are discussed.

The heme environment of leghemoglobins. Absorption and circular dichroism spectra of artificial leghemoglobins and myoglobins

Artificial leghemoglobins were reconstituted from apoleghemoglobin and meso-, deutero- and diacetyldeuteroheme. Absorption and circular dichroism spectra of their high-spin and low-spin derivatives in the ferrous and ferric forms were recorded in the ultraviolet and visible wavelength regions. The substitution of the 2,4-side-chains of heme induced changes in the optical activity, reflecting alterations in the heme environment. The effect on the conformation of aromatic amino acid residues around heme obviously correlates with the sixth axial ligand and the spin state of iron. Absorption and CD spectra of the aquoferric derivatives of artificial myoglobins were recorded in comparison. Strongly electron-withdrawing acetyl side-chains at the 2,4-positions of diacetyldeuteroheme caused a change in the absorption spectra of aquoferric leghemoglobin and myoglobin towards low spin. On the basis of the spectra it was suggested that the displacement of the ferric iron from the pyrrole plane in leghemoglobin derivatives would be smaller than in the corresponding myoglobin derivatives.

Determination of plasma or serum haemoglobin by peroxidase activity employing 2,2'-azino-di-(3-ethyl-benzthiazolinsulphonate-6) as chromogen

A procedure is described for the determination of plasma or serum haemoglobin employing the peroxidase activity of the haemoprotein using 2,2'-azino-di-(3-ethyl-benzthiazolinsulphonate-6) as chromogen. The method gives equal results for free haemoglobin, methaemoglobin and haemoglobin complexed to haptoglobin. It is designed to measure haemoglobin in the range 0--12 mumol/l. The peroxidase activity of myoglobin is similar to that of haemoglobin, whereas haemin in free solution, bound to haemopexin or to albumin (methaemalbumin) shows much lower activity. The precision within run is satisfactory, +/- 5%.

Heat inhibition of reticulocyte protein synthesis. Evidence for a mechanism independent of the hemin-controlled repressor

Incubation of rabbit reticulocytes at 45 degrees C results in a prompt but reversible decrease in protein synthesis and a concomitant conversion of polyribosomes to smaller aggregates. These effects occur even in the presence of 100 micrometer hemin in the incubation medium. There is also inhibition of heme synthesis but this occurs at a later time than the effect on protein synthesis. The inhibtion of heme synthesis results from a decrease in activity of beta-aminolevulinic acid synthetase. This decrease of heme synthesis appears to be secondary to the inhibition of protein synthesis with resultant accumulation of intramitochondrial heme (which will decrease beta-aminolevulinic acid synthetase activity). An inhibitor of reticulocyte cell-free protein synthesis formed in the postribosomal supernatants of cells incubated at both 45 and 37 degrees C but not at 0 degrees C. No temporal or quantitative differences in the amount of this inhibitor from cells treated at either 37 or 45 degrees C was apparent. The inhibitor was not found in the fraction where the hemin-controlled repressor is isolated. It is concluded that heat inactivation of intact reticulocyte protein synthesis does not depend upon a decrease in heme synthesis, heme concentration or generation of the hemin-controlled repressor. Furthermore, it appears that the inhibitor formed in the post-ribosomal supernatant cannot be the sole cause of the heat inhibition of protein synthesis.

Induction of globin mRNA accumulation by hemin in cultured erythroleukemic cells

The role of heme in erythroid development is investigated in erythroleukemic (Friend) cells. Exogenous hemin induces the accumulation of globin mRNA and globin protein in T3-C12 erythroleukemia cells to levels comparable to those induced by polar solvents, such as dimethylsulfoxide (DMSO). The hemin concentration required for maximal induction (10(-4) M) is the same as that which stimulates globin message translation in reticulocytes or cell-free reticulocyte lysates. Hemin and DMSO together cause T3-C12 cells to accumulate 8-9 fold more globin mRNA than either inducer individually. The kinetics of globin mRNA induction in hemin as compared to DMSO are very different: globin message accumulation begins 4 hr after hemin addition, but not until 30--40 hr after DMSO addition. Biliverdin induces 20--40 fold less hemoglobin than hemin; delta-aminolevulinic acid and porphobilinogen do not induce.