FLUOROMETRIC MICRODETERMINATION OF HEME PROTEIN

Accumulation and drainage of hemin in the red cell membrane

The subject of hemin intercalation in red cell membranes and the correlation of the accumulated hemin level with the membrane pathology was studied. Methods which made use of dioxan and octan-2-ol mixtures to quantitate small amounts of hemin in membranes were developed. Applying these methods, hemin levels were measured in the cytoskeleton and the remaining lipid core of various red cell membranes. The amount of hemin, in both membrane fractions, was higher in pathological cells of sickle cell anemia and beta-thalassemia as compared to normal circulating cells. Correlation exists between the amount of the membrane-accumulated hemin and the severity of the disease. The level of hemin in the membrane was found to be age dependent, old cells in circulation accumulating more hemin than young cells. The level of hemin in all cells tested was much lower than the amount found previously to cause immediate hemolysis when applied externally (Kirschner-Zilber, I., Rabizadeh, E. and Shaklai, N. (1982) Biochim. Biophys. Acta 690, 20-30). This was explained by the differences between the process leading to immediate lysis and membrane changes recognized as pathological by the in-vivo sequestration mechanism. In search of a physiological mechanism which may drain the cell membrane from the hazardeous hemin, albumin, the main serum protein, was found capable of serving as an efficient agent for extracting hemin trapped in red cell membranes. It is suggested that under normal conditions albumin extracts enough hemin to leave the erythrocyte with unharmful hemin amounts, however, under pathological conditions greater amounts accumulate leading to a shorter cell life span.

The influence of carbamazepine on the heme biosynthetic pathway

Carbamazepine, a drug which is widely used in neurological diseases, has a porphyrogenic effect in chick embryo liver cells in culture. It increased the concentration of cellular porphyrins by 80-fold and delta-aminolevulinate synthase activity by 4-fold. The increase in the accumulation of porphyrins preceded that of ALAS activity. Measurements of the activities of aminolevulinate dehydrase, porphobilinogen deaminase, and uroporphyrinogen decarboxylase showed that C inhibits UROD up to nearly 50% and PBGD activity up to 20%, but does not affect the activity of ALAD. The pattern of accumulation of porphyrins, mainly uro- and heptacarboxylporphyrin, is compatible with an inhibition of UROD. We may, therefore, conclude that the porphyrogenic effect of C in monolayers of chick embryo liver cells is the result of its inhibitory effect on the activity of UROD.

Heme requirement and acquisition by extracellular and intracellular stages of Leishmania mexicana amazonensis

The inability to synthesize heme, a well known metabolic defect of trypanosomatid protozoa, accounts for their growth requirement for heme compounds in vitro. We now extend this finding to a pathogen Leishmania mexicana amazonensis, especially the intracellular replicative stage of amastigotes in the macrophage. We measured the level of heme and its biosynthetic enzymes, aminolevulinate dehydratase and porphobilinogen deaminase in the parasites and in infected and non-infected macrophages of J774G8 line. Succinylacetone was used to inhibit heme biosynthesis. Leishmanias transform and grow only in medium containing either heme (usually supplied as hemin) or protoporphyrin IX (the latter is leishmanicidal at high concentrations). We detected 1.2, 8.5 and 25 pmol mg-1 protein of heme in amastigotes, promastigotes and macrophages, respectively. The activities of porphobilinogen deaminase and aminolevulinate dehydratase in macrophages were 70 and 2400 pmol h-1 mg-1 protein, respectively. Leishmania-infected macrophages gave the same results and leishmanias had negligible activities of these enzymes. Succinylacetone at 10(-9)-10(-3) M had no effect on leishmanias, but dose-dependently inhibited the activity of aminolevulinate dehydratase to a negligible level and lowered that of porphobilinogen deaminase in macrophages, resulting in a maximum of 66% reduction in intracellular heme. Amastigotes grew equally well in succinylacetone-treated and control untreated macrophages. The results suggest that L. m. amazonensis, incapable of heme biosynthesis, acquires heme exogenously from the culture medium, i.e., fetal bovine serum, independent of the heme synthesized by the macrophages.

A characterization of haem uptake and intracellular distribution by isolated hepatocytes

The uptake and intracellular distribution of haem by isolated rat hepatocyte suspensions was studied. An increase in cell haem content occurred after a challenge with 5, 10 or 20 microM haem, supplied as methaemalbumin. The rate of haem uptake was temperature dependent; no non-specific binding occurred. Intracellular haem distribution data are consistent with a rapid association of haem with the endoplasmic reticulum fraction prior to its accumulation in the cytosol and at the mitochondrion.

The effects of lead on differentiation of the Friend leukemia cells and rat bone marrow cells

The effects of lead toxicity on differentiation of erythroid cells was examined using Friend leukemia cells induced with 2% dimethyl sulfoxide. By increasing the concentration of lead, these cells exhibited a lag before the onset of induction. When incorporation of [3H]-delta-aminolevulinic acid into heme was compared, the maximum incorporation into the cells without lead was on the third day after induction, while it was on the fifth day in the presence of lead (5 X 10(-4) M). However, these cells did reach similar differentiation stages by the seventh day. The amount of delta-aminolevulinic acid which was excreted into the medium increased in the presence of more than 10(-4) M lead. The amount of coproporphyrin III was slightly increased with 10(-6) M lead. Protoporphyrin IX content in the cells decreased slightly with increasing concentrations of lead. delta-Aminolevulinic acid dehydratase activity in cells which were cultured in the presence of lead was low, while synthesis of this enzyme increased in the presence of lead. The bone marrow cells from lead-poisoned rats exhibited a lag in onset of maturation, which was consistent with the effect of lead on Friend cells.

The effects of metalloporphyrins, porphyrins and metals on the activity of delta-aminolevulinic acid synthase in monolayers of chick embryo liver cells

The effect of various metals, porphyrins and metalloporphyrins on the activity of delta-aminolevulinate synthase (ALAS) was measured in monolayers of chick embryo liver cells in order to determine whether the metal moiety of heme or heme itself is the regulator of ALAS activity. Iron, magnesium, zinc, copper, manganese and nickel did not decrease ALAS activity in non-induced and in cells induced by allyl-isopropylacetamide (AIA). Cobalt decreased both non-induced and induced activity. Porphyrins inhibited ALAS, apparently only after having been converted into metalloporphyrins. Almost all the metalloporphyrins examined decreased ALAS activity. None of the substances, at the concentrations used, was toxic to the cells. These observations indicate that probably heme and not iron is the regulator of ALAS activity in monolayers of chick embryo liver cells.

The interaction of hemin with skeletal muscle actin

The ability of actin to interact with hemin was studied. It was found that the Soret absorption band of hemin changes in the presence of actin and that hemin is capable of quenching the fluorescence intensity of actin. These findings were indicative of hemin binding to actin. The binding constant for the high affinity site was calculated to be 5.3 X 10(6) M-1. The amounts of native G- and F-actin were estimated by their DNAase I inhibition activity. It was observed that the binding of hemin to G-actin is followed by a slow decrease in the ability of actin to inhibit DNAase I activity and to polymerize upon addition of salts. Binding of hemin to F-actin resulted in a gradual depolymerization of the filaments, to an inactivated form, as expressed by a reduction in the ability of hemin-bound F-actin to inhibit DNAase I activity in the absence as well as in the presence of guanidine-HCl. Electron microscopy studies further corroborated these findings by demonstrating that: (1) hemin-bound G-actin failed to show formation of polymers when salts were added; (2) a marked reduction in the amount of actin polymers was observed in the specimens examined 24 h after mixing with hemin. It is suggested that the elevated amounts of free hemin formed under pathological conditions, might be toxic to cells by interfering with actin polymerization cycles.

The effects of succinylacetone (4,6-dioxoheptanoic acid) on delta-aminolevulinate synthase activity and the content of heme in monolayers of chick embryo liver cells

Succinylacetone was shown to inhibit aminolevulinate dehydratase (5-aminolevulinate hydro-lyase (adding 5-aminolevulinate and cyclizing), EC 4.2.1.24) to reduce cellular heme and porphyrins and to induce delta-aminolevulinate synthase (succinyl-CoA:glycine C-succinyltransferase (decarboxylating), EC 2.3.1.37) in monolayers of chick embryo liver cells. Marked synergistic effects on delta-aminolevulinate synthase activity were obtained by combining succinylacetone with levulinate and porphyrogenic drugs. The time course of delta-aminolevulinate synthase activity showed a delayed synergistic response.

Decreased heme content and cessation of cell growth in cultured chick embryo fibroblasts in the presence of horse serum: stimulation of heme synthesis and cell growth by iron

A new spectrofluorometric method for heme quantitation in cultured fibroblasts is described. The method includes: 1) heme extraction by methanol/sulfuric acid, 2) partial purification of heme by a microchromatographic method, and 3) treatment of the purified heme by oxalic acid followed by fluorometric quantitation. Using this method, heme concentration was determined in chick embryo fibroblasts cultured in a medium supplemented with either 7% fetal bovine serum (FBS) or 10% horse serum (HS). In the presence of FBS, cultured cells actively divided and cells contained 34-55 pmol heme/mg protein. In contrast, cultures maintained in HS proliferated at a slower rate and contained 23-25 pmol heme/mg protein. The addition of 40 microM FeSO4 to cultures maintained in the presence of HS stimulated cell proliferation, and the cellular heme concentration increased to 37-51 pmol/mg protein. These findings suggest that the cessation of growth in the presence of HS may be due to decreased heme content in the cells and that the stimulation of cell growth by iron is mediated by its stimulation of heme synthesis.

The turnover of cytochrome P450b

The turnover of the heme and apocytochrome moieties of phenobarbital-inducible microsomal cytochrome P450 (P450b) was investigated. Adult male Sprague-Dawley rats were treated with phenobarbital for 5 days and injected with [35S]methionine and the heme precursor delta-[3H]-aminolevulinic acid. P450b was isolated by immunoprecipitation and quantitated by rocket immunoelectrophoresis. The isotope disappearance curves revealed a mean half-life (T1/2) of 12.4 h for the heme moiety and a T1/2 of 19.1 h for the apoprotein moiety of P450b. The apparently slower catabolic rate of the apoprotein may be due to reutilization of [35S]methionine and does not exclude synchronous turnover of the two moieties. Our data are consistent with the kinetics of the drug-mediated induction of cytochrome P450b.

The interaction of hemin and bilirubin with the human red cell membrane

The incubation of 0.5% suspension of fresh normal erythrocytes with hemin or bilirubin resulted in substantial hemolysis. The amount of hemolysis achieved depended on the concentration of the lytic agents. In each concentration maximum hemolysis was reached within half an hour. The hemolytic effect was somewhat dependent on temperature. Comparison with the hemolytic effect of hemin on mice (Chau, A.C. and Fitch, C.D. (1980) J. Clin. Invest. 66, 856-858) showed that although both cells undergo hemolysis by hemin, the behaviour of each red cell type is different. Centrifugation and fluorescence quenching of membrane embedded probe revealed that both hemin and bilirubin bind to the red cell membrane, hemin having higher affinity. The reaction was found to be hydrophobic and therefore independent of ionic strength. The high affinity of the membrane for hemin was shown by its ability to compete successfully with globin for hemin. Electron microscopy of the red cells which underwent hemolysis indicated cell damage and some membrane destruction. Red cell ghosts were totally disrupted when saturated with hemin. These results suggest an explanation for hemolytic events occurring in cases such as elevation of serum bilirubin or abnormalities leading to hemin release by hemoglobin.

The influence of propranolol on the concentration of heme and on the activity of delta aminolevulinate synthase in monolayers of chick embryo liver cells

The addition of propranolol to monolayers of chick embryo liver cells caused a rapid increase in cellular heme, followed by an equally rapid decrease. Subsequently the concentration of heme rose at a relatively slower rate. About 10 hr after addition of propranolol to the medium a plateau level was reached at +/- 35% above control values. Changes in the activity of delta-aminolevulinate synthase (ALAS) were negatively correlated with those of cellular heme. Cycloheximide prevented the above phenomenon. ALAS activity was not clearly correlated with the rapid, partial inhibition of protein synthesis, caused by propranolol. These observations are related to the beneficial influence of administration of hemin or of propranolol to patients with acute attacks of hepatic porphyria.

Heme content of normal and porphyric cultured skin fibroblasts

Partial deficiencies in enzyme activities of the heme biosynthetic pathway have been demonstrated in cultured skin fibroblasts and other tissues from patients with protoporphyria (PP) and acute intermittent porphyria (AIP). We have quantitatively and qualitatively assessed the heme and free porphyrin content in cultured PP, AIP, VP (variegate porphyria, in which an enzymatic deficiency has not been identified), and normal skin fibroblasts during routine culture conditions in order to assess the overall metabolism of heme in these cells. The total heme concentration was not significantly different between control and porphyric lines; 189 +/- 15 pmoles/mg protein (mean +/- SEM) in controls, 154 +/- 17 in PP, 175 +/- 20 in AIP, and 181 +/- 81 in VP. The hemoprotein difference spectra were similar in all lines. Free porphyrins were not detected in any of the disorders. Despite partial deficiencies in enzyme activities of the heme pathway, porphyric fibroblasts thus maintain normal heme content during routine culture conditions without detectable porphyrin accumulation.

Sequential induction of heme pathway enzymes during erythroid differentiation of mouse Friend leukemia virus-infected cells

The process of erythroid differentiation in mouse Friend leukemia virus transformed cells (T3-C1-2) was examined by following changes in several enzyme activities of the heme biosynthetic pathway and in heme concentration while the cells were undergoing erythroid differentiation after treatment with dimethylsulfoxide. Untreated cells on the one hand, have a limited capacity for spontaneous differentiation. On the other hand, dimethylsulfoxide(DMSO)-treated cells showed an increase in the activities of delta-aminolevulinic acid (ALA) synthetase, ALA dehydratase, uroporphyrinogen-I synthetase, ferrochelatase, and heme concentration by days 1, 1.5, 2, and 4, respectively. The increase of the heme pathway enzymes and heme concentration followed the order of these enzymes or products as they are arranged in the heme biosynthetic pathway. These changes induced by DMSO were effectively inhibited by treatment with actinomycin D, suggesting that continued RNA synthesis is required for the differentiation process. 5-bromo-2'-deoxyuridine (BrdU) (10(-5) M) inhibited the DMSO-induced changes of the heme pathway enzymes. BrdU was most effective when it was present during the first 2 days of cell culture. It gradually lost its inhibitory effect when added after the 3rd day or later. The BrdU-mediated inhibition was completely overcome by the addition of thymidine (7 x 10(-5) M), but not by uridine (7 x 10(-5) M). All these data suggest that a sequential induction of the heme pathway enzyme takes place during erythroid differentiation of Friend leukemia cells, and that the sequential induction of the enzymes may be due to a sequential activation of genes coding for these enzyme activities.