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Biomedical subjects

U Muller-Eberhard

Publications and source records attributed to U Muller-Eberhard.

At least 127 records · Page 7Linked to original sources
PubMed1976

The aromatic and heme chromophores of rabbit hemopexin. Difference absorption and fluorescence spectra.

Spectrophotometric and fluorimetric techniques were employed to charcterize the environment of the heme chromophore of rabbit hemopexin and to monitor changes in the environment of aromatic amino acid residues induced by the interaction of hemopexin with porphyrins and metalloporphyrins. Difference spectra showed maxima at 292 and 285 nm when hemopexin binds heme or deuteroheme but not deuteroporphyrin. These maxima are attributed to alterations in the local environment of tryptophan and tyrosine residues. Spectro-photometric titrations of the tyrosine residues of hemopexin, heme-hemopexin and hemopexin in 8 M urea showed apparent pK values at 11.4, 11.7, and 10.9 respectively. Perturbation difference spectra produced by 20% v/v ethylene glycol are consistent with the exposure of 6-8 of the 14 tyrosine residues and 6-8 of the 15 tryptophan residues of rabbit hemopexin to this perturbant. Only small differences were found between the perturbation spectra of apo- and heme-hemopexin near 290 nm, suggesting that slight or compensating changes in the exposure to solvent of tryptophan chromophores occur. In the Soret spectral region, the exposure of heme in the heme-hemopexin complex to ethylene glycol was 0.7, relative to the fully exposed heme peptide of cytochrome c. The fluorescence quantum yields of rabbit apo- and heme-hemopexin were estimated to be 0.06 and 0.03, respectively, compared to a yield of 0.13 for L-tryptophan. Iodide quenched 50% of the fluorescence of the deuteroheme-hemopexin complex. Cesium was not an effective quencher. Modification of approximately, 4 tryptophan residues with N-bromosuccinimide also decreased the relative fluorescence of apo-hemopexin by 50% and concomitantly reduced the heme-binding ability of the protein by 70%. The existence of sterically unhindered tryptophan residues in either apo- heme-hemopexin is unlikely since no charge transfer compelxes between these proteins and N-methylnicotinamide were detected.

Animals↗
PubMed1976

Synthesis of hemopexin with and without hormonal supplementation in rat hepatocyte suspensions: comparison with that of albumin and of fibrinogen.

The rate of hemopexin synthesis in adult rat hepatocyte suspension (0.17 +/- 0.019 (6)) (mean +/- SEM (n) mg/g hepatocytes per hour) was found to be linear for 48 h. By contrast, the rate of synthesis of albumin and fibrinogen was close to linear for only 12 h after which it continued at a diminished rate. Supplementation of the incubation medium with insulin, cortisol, glucagon, triiodothyronine, and growth hormone affected no significant increase in the synthesis rate of hemopexin but by contrast did do so in that of albumin (22%) and of fibrinogen (123%) (although not to the point of causing these last to become linear). The pattern of hemopexin synthesis and its response to hormones is clearly different from that observed with other plasma proteins studied in this hepatocyte system. Hempoexin synthesis appeared to be at its maximum and to be independent of hormone supplementation, and it was continuing linearly at a time when the synthesis of other plasma proteins was falling.

Albumins↗
PubMed1976

Genetic control of serum hemopexin.

Serum hemopexin was studied in a sample of twin pairs. Among monozygotic twin pairs a high concordance was found for serum hemopexin. This zygosity group analysis of variance also showed a significantly lower variance within than between pairs. The results indicate that the concentration of serum hemopexin is strongly influenced by genetic factors.

Analysis of Variance↗
PubMed1975

Interaction of rabbit hemopexin with rose bengal and photooxidation of the rose bengal-hemopexin complex.

Rabbit hemopexin associates with rose bengal producing a hypochromic shift in the absorption spectrum of the dye; the extinction coefficient of the dye bound to heme-saturated hemopexin is approximately 20% lower than that of the dye bound to the apoprotein. The interaction of apo- and heme-saturated hemopexin with rose bengal was studied in detail by difference spectroscopy. Apo-hemopexin has one tight binding site for the dye with a dissociation constant in the micromolar range and a set of several weaker binding sites. In contrast, heme-saturated hemopexin has a very low affinity for the dye. Evidence that histidine residues of hemopexin participate in the binding of heme was obtained by photooxidation of hemopexin sensitized by rose bengal. Progressive modification of the 16 histidine residues of hemopexin is effected by illumination of the dye-hemopexin complexes. The midpoint of this pH-dependent reaction is at pH 6.8 +/- 0.1. In 15 min of irradiation, apo-hemopexin loses 50% of its ability to form a low spin hemichrome complex with deuteroheme while only 10% of the ligand coordination to heme iron of the deuteroheme-hemopexin is lost. At that time, approximately 2 more histidine residues are modified in apo-hemopexin than in deuteroheme-hemopexin, and no change is found in other potentially photolabile amino acid residues. The characteristic circular dichroism positive extremum at 231 nm of hemopexin also was decreased by photooxidation, and the loss was slower in the deuteroheme-hemopexin complex than in the apoprotein. When deuteroporphyrin IX was used as the photosensitizing agent, similar results were obtained.

Animals↗
PubMed1975

Relationship of the biosynthesis of alpha-fetoprotein, albumin, hemopexin, and haptoglobin to the growth state of fetal rat hepatocyte cultures.

AFP and albumin are produced by arginine-synthesizing fetal rat hepatocytes in vitro. AFP and hemopexin production are coupled to hepatocellular proliferation, whereas albumin and haptoglobin production are not. During the cell cycle, AFP is synthesized prior to S and released prior to M. AFP may play a role in regulation of hepatocellular growth through estradiol binding and modulation of the intracellular concentration of lipoprotein (VLDL).

Albumins↗
PubMed1975

Interaction of rabbit hemoplexin with copro- and uroporphyrins.

Rabbit hemopexin forms equimolar complexes in vitro with the I and III isomers of both coproporphyrin and uroporphyrin. The apparent dissociation constants (Kd) of these complexes are estimated to be 4-10(-7) M for coproporphyrin-hemopexin and 10(-6) M for uroporphyrin-hemopexin by equilibrium dialysis and quenching of protein fluorescence. Results of competitive binding experiments suggest that all four porphyrins bind at the heme-binding site of hemopexin, and that the relative affinity of rabbit hemopexin for these porphyrins is: deuteroheme greater than coproporphyrin I or III greater than uroporphyrin I or III. These findings provide further evidence that hemopexin may function as a transport protein for circulating coproporphyrins as well as for heme.

Animals↗
PubMed1975

Catabolism of photo-oxidized and desialylated hemopexin in the rabbit.

Following injection of rabbit 125I-asialohemopexin, more than 90% of the protein-bound 125I was removed from the circulation of rabbits within 12 min. The amount of asialoprotein in the catabolic compartment reached a peak concentration (75 to 85%) 12 min after injection and was completely eliminated from this compartment within 2 hours. The degradation products were excreted into the urine, with 50 to 70% of the 125I eliminated during the first 24 hours and 90 to 95% excreted by 48 hours. Analysis of these data indicated an apparent first order rate constant for uptake of asialohemopexin of 0.32 min-1, for catabolism of 0.020 min-1 and for excretion of 0.054 to 0.093 hour-1. The plasma distribution curves of 125I-hemopexin, after the first 24 hours, showed essentially no difference. Both proteins were catabolized with an average T1/2 of 25 to 26 hours and a similar fractional catabolic rate. Simultaneous injection of heme and 125I-hemopexin resulted in rapid removal and catabolism of the protein. In contrast, injection of heme had little if any effect on the plasma radioactivity curve of photoinactivated 125I-hemopexin.

Animals↗
PubMed1975

Cellular and subcellular localization of heme and hemopexin in the rabbit.

The cellular distribution of intravenously administered 3H-heme, 125I-hemopexin and 125I-albumin was studied in rabbits. Radioautography of the tissue slides of several organs was examined by light and electron microscopy. All experiments were terminated 60 min after injection of the isotope-labeled materials. 3H-heme and native monomeric 125I-hemopexin (heme saturated) were found to be associated with the endoplasmic reticulum and microbodies of the hepatocytes. Aggregated hemopexin was also taken up by macrophages of lung alveoli, splenic pulp, interstitial cells of the kidney and Kupffer cells. 125I-albumin (heme saturated) could not be located in liver, spleen, bone marrow, lung, or kidney tissues.

Animals↗
PubMed1975

Hemopexin synthesis in vitro by human fetal tissues.

Serum concentrations of hemopexin, transferrin, and albumin were measured for 12 fetuses between 14 and 36 weeks of gestational age. Hemopexin levels ranged from 7 to 64 mug/ml, transferrin levels ranged from 280 to 928 mug/ml, and albumin levels ranged from 13 to 59 mg/ml. In general, the serum concentrations of these three proteins increased with advancing gestation. Placenta, thymus, and colon did not incorporate 14C-labeled amino acids into hemopexin, transferrin, or albumin. By contrast radioimmune precipitates for five culture supernatants of liver indicated significant synthesis of albumin and hemopexin. [14C]Albumin accounted for 22-73% and [14C]hemopexin 1.1-4.2% of the total 14C-labeled proteins. In each instance, the [14C]transferrin was below 1% of the total 14C-labeled proteins.

Amino Acids↗
PubMed1975

Effect of hemoglobin and hematin on plasma clearance of hemopexin, photo-inactivated hemopexin and albumin (38575).

The plasma half clearance time (T1/2) of isotope-labeled rabbit hemopexin was 35.5 plus or minus 1.9 hr in rabbits. After intra-and extra-vascular equilibration of 125I-hemopexin and 131I-albumin, injection of either hematin, hemoglobin or methemoglobin (12.5 mg of heme/kg body wt) resulted in the rapid removal of 60-80% of circulating hemopexin (T1/2 = 7.2 plus or minus 0.6 hr) but did not affect albumin catabolism. After selective photo-inactivation of hemopexin, the T1/2 of this hemopexin was comparable to that of the native molecule. However, its plasma disappearance curve was not appreciably affected by administration of hematin. These findings demonstrate that hemopexin is cleared and catabolized at an enhanced rate during states of plasma heme load, and that modification of critical histidine residues of hemopexin eliminates its biological function in plasma heme disposal.

Animals↗
PubMed1975

Synthesis of plasma haemopexin, albumin and fibrinogen by the regenerating rat liver.

The concentration of plasma haemopexin was significantly increased 24 and 48 h following both partial hepatectomy and laparotomy in the rat. Increased haemopexin synthesis was demonstrated by studies on the in vivo incoporation of isotope labelled amino acids and in vitro perfusion of the isolated liver. In vivo studies also indicated increased synthesis of plasma fibrinogen. No change was found in the incorporation of amino acids into plasma albumin apart from a transient rise 4 h after laparotomy but albumin production by the perfused rat liver 48 h after partial hepatectomy appeared enhanced. The observed changes in rat haemopexin and fibrinogen synthesis may represent a nonspecific acute phase response to surgical trauma.

Amino Acids↗