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J Awruch

Publications and source records attributed to J Awruch.

14 recordsLinked to original sources
PubMed1999

Exploring the conformation of bilirubins with natural and unnatural analogues: use of positional and bridged isomers of bilirubin IXalpha.

Unlike bilirubin IXalpha (1), the isomers bilirubin IXdelta (2) and neobilirubin IXbeta (3) do not require conjugation with glucuronic acid in order to be excreted. A conformational analysis employing an optimized Monte Carlo method and a mixed Monte Carlo stochastic dynamics reveals that isomer 2 exhibits a structure more closed than the well known 'ridge-tile' conformation of 1. The change in the position of both propionic acid chains causes the loss of at least four hydrogen bonds. On the other hand, the change in the configuration of the distal dipyrrinone and the blockage of the lactamic nitrogen by the presence of a bridge in isomer 3 results in an open and more elongated structure, where the chance of hydrogen bond formation in this region is obliterated. The resulting molecular models for these compounds are consistent with 1H NM R, UV-vis, and TLC data.

Animals↗
PubMed1998

Probing the conformation of bilirubins with monopropionic analogs: a biological, spectroscopic, and molecular modeling study.

The in vivo metabolism of a bilirubin analog substituted with a propionic acid chain in C8 (5) showed that it is excreted in bile conjugated with glucuronic acid, while a positional isomer substituted with a propionate in C7 (6) is excreted in bile without conjugation. A conformational analysis employing an optimized Monte Carlo method and a mixed Monte Carlo/stochastic dynamics reveals that isomer 5 adopts a 'ridge tile' conformation, stabilized by the presence of three intramolecular hydrogen bonds. On the contrary, isomer 6 exhibits a more closed structure, where impairment in the formation of at least one of the hydrogen bonds occurs. These theoretical predictions agree well with 1H NMR, UV-vis, and TLC data.

Bilirubin↗
PubMed1997

Synthesis and photophysical properties of a new cationic water-soluble Zn phthalocyanine.

The synthesis of tetrakis (1,1-dimethyl-2-trimethylammonium)ethylphthalocyaninato Zn(II) tetraiodide 2--a new cationic phthalocyanine--is reported as well as its photophysical properties in water, relevant for the use of this dye as photodynamic sensitizer. The hydrophobicity of the macrocycle leads to strong aggregation which lowers the fluorescence and singlet oxygen quantum yields of aqueous solutions of 2. Photophysical parameters agree with those of other Zn phthalocyanines when correction is performed for the fraction of light absorbed by the monomer.

Cations↗
PubMed1994

Degradation of heme IX in rats pretreated with cobaltous chloride. A study in isolated perfused liver.

The effect of the administration of cobaltous chloride on the degradation of heme IX was investigated using perfusions of isolated rat livers. The presence of biliverdin IX beta (2%) in the bile fluid of cobaltous chloride treated rats support the hypothesis of the presence of a chemical oxidation of heme IX induced by the cobalt salt. In control rats the absence of biliverdin IX beta in the bile fluid was observed. When biliverdin IX beta was added to the perfusate it was excreted in the bile fluid as bilirubin IX beta without conjugation. An increase from approximately twofold to three-fold of the total bilirubins in the bile fluids of cobaltous chloride pretreated rats in relation with control rats was observed due to heme oxygenase enhanced activity. Bilirubin IX alpha diconjugates increased ca. 15% in the bile fluids of cobaltous chloride pretreated rats, after the addition of hemin IX. The increase could reflect the presence of a new molecular form of UDP-glucuronosyltransferase, which favours the formation of bilirubin IX alpha diglucuronide and therefore its preferential excretion into the bile. In the bile fluid of the rats pretreated with cobaltous chloride, other diconjugates of bilirubin IX alpha were also detected 120 min after the addition of hemin IX to the perfusate, consisting of glucose and glucuronate (5%) and xylose and glucuronate (5%).

Animals↗
PubMed1987

Biliverdin reductase: substrate specificity and kinetics.

The substrate specificity of the different forms of rat liver biliverdin reductase was examined using synthetic biliverdins. Biliverdins carrying methyl, ethyl and one propionate residue in their structure were not substrates of biliverdin reductase. Biliverdins with one propionate and one acetate residue or with two acetate residues were not reduced by the enzyme either. The presence of two propionates in the biliverdin structure gave a biliverdin with substrate activity. Increasing the number of propionates to four, as in coprobiliverdins, did not affect substrate activity, while the octaacid urobiliverdins were also good substrates of the enzymes. The beta isomer of urobiliverdin III and coprobiliverdin III were reduced at much higher rates by molecular form 3 of the enzyme as compared to molecular form 1, a fact which had already been observed with the beta isomer of biliverdins IX, XIII and hematobiliverdin. All the biliverdins mentioned above were readily reduced to bilirubins by sodium borohydride. The purified molecular forms 1 and 3 displayed sigmoidal kinetics with most of the biliverdins tested. The data were analyzed by nonlinear regression in a microcomputer and it was found that they fitted a model of a moderate cooperative dimer where both ES and ES2 are catalytically active. The Vm, Ks and the Hill numbers, nH, for biliverdin IX alpha and beta, hematobiliverdin IX alpha and beta, and several synthetic biliverdin isomers are given. Molecular form 2 showed classical Michaelian kinetics.

Algorithms↗
PubMed1984

The specificity of biliverdin reductase. A study with different biliverdin types.

The specificity of rat liver biliverdin reductase was examined with the help of a series of synthetic biliverdins. The mixture of the four biliverdin isomers obtained by the chemical oxidation of protohemin I, protohemin XI, protohemin XIV and harderohemin were used as substrates of biliverdin reductase and were compared with the mixture of biliverdins IX alpha-delta. Biliverdin reductase (molecular form 1) from rat liver efficiently reduced the isomer mixtures of biliverdins I, XI, XIV and harderobiliverdins to the bilirubins in the presence of NADPH. The enzymatic reduction of the different biliverdin types was studied in the presence of different NADPH analogues. NADPH could be replaced by NADH, 3-acetyl NADPH and deamino-NADPH with retention of a good substrate activity only in the case of biliverdins of types I and IX and harderobiliverdins. Biliverdins XI and XIV were efficiently reduced only in the presence of NADPH and an excess of NADH. Bactobilin III-alpha was also very efficiently reduced by biliverdin reductase in the presence of both NADPH and NADH but not in the presence of the other analogues. These results indicate that biliverdin reductase reduced bilitriene acids substituted with non-polar and polar residues.

Animals↗
PubMed1984

The specificity of biliverdin reductase. The reduction of biliverdin XIII isomers.

The substrate specificity of the different molecular forms of biliverdin reductase (bilirubin:NAD(P)+ oxidoreductase, EC 1.3.1.24) using biliverdin XIII alpha, XIII beta and XIII gamma was examined. It was found that molecular form 1 (the major form in normal rat liver) reduced biliverdin XIII alpha at a much higher rate than the other two isomers. Molecular form 2 (the minor form) reduced isomers XIII alpha and XIII beta at similar rates, while molecular form 3 (the major form induced by CoCl2 treatment) reduced the XIII beta isomer at a slightly higher rate than the XIII alpha isomer. Molecular forms 2 and 3, both reduced isomer XIII gamma more slowly than they reduced the XIII alpha and XIII beta isomers. These results are similar to those obtained previously using biliverdins IX alpha, IX beta and IX gamma, suggesting that biliverdin reductase specificity is related to the type of the isomer rather than to the series (IX or XIII) of the isomer.

Animals↗
PubMed1984

Isolation from rat liver of a peroxisomal enzyme which converts molecular form 1 of biliverdin reductase into molecular form 3.

Cobaltous chloride induced in rat liver an enzyme which converted biliverdin reductase molecular form 1 into the molecular form 3. This conversion involves the oxidation of two sulfhydryl groups of form 1 giving rise to a disulfide bond in form 3. The converting enzyme was isolated from the liver peroxisomal fraction (which was devoid of biliverdin reductase activity), and was absent in liver peroxisomes of control rats. The enzyme was solubilized by treatment of the peroxisomes with 0.1% sodium deoxycholate, and partially purified by DEAE-cellulose and Sephadex G-100 filtration. It is a NAD+ dependent enzyme which was inactivated by trypsin and heat treatments. It did not oxidize either reduced glutathione or cysteine. The converting enzyme had a molecular weight of about 54,000 daltons. The oxidation of biliverdin reductase molecular form 1 mediated by the converting enzyme did not affect the latter's molecular weight or activity.

Animals↗
PubMed1983

Interconversion of the molecular forms of biliverdin reductase from rat liver.

Rat liver biliverdin reductase exists in two molecular forms. The major molecular form 1 has a high reduction rate for biliverdin IX alpha, while the minor molecular from 2 has high reduction rates for both biliverdins IX alpha and IX beta. The major molecular form 1 was gradually transformed into a second major form (form 3) by treatment of the rats with CoCl2. Form 1 reduces biliverdin IX alpha at two and a half times the rate of biliverdin IX beta while form 3 reduces both isomers at about the same rate. This transformation involves a de novo mRNA and protein synthesis since it could be prevented by cycloheximide and actinomycin D. Molecular form 3 can be transformed back into molecular form 1 by an in vitro treatment with reduced thioredoxin. Phenylhydrazine treatment also induced the transformation of molecular form 1 into molecular form 3 in rat liver. Biliverdin reductase from rat spleen and kidney exists only in molecular form 1 and is not transformed into molecular form 3 by either CoCl2 or phenylhydrazine treatments.

Animals↗
PubMed1982

Degradation of hemin IX and synthetic hemins to alpha-bilirubins and their conjugates in the isolated perfused rat liver.

Hemin IX was perfused through rat liver of a normal, untreated animal. Its degradation products, collected in the bile fluid over a period of 90 min, were found to consist of the bilirubin IX-alpha diglucuronide (56%), the mixture of bilirubin IX-alpha monoglucuronides (42%), and free bilirubin IX-alpha (2%). When the synthetic hemin XIII 2 was perfused with the same technique, it was found to be degraded in the same way. The bile fluid contained the diglucuronide of bilirubin XIII-alpha 10 (55%), the monoglucuronide of bilirubin XIII-alpha 9 (43%) and the free bilirubin XIII-alpha 8 (2%). Similar results were obtained when the iron 1,4-di(beta-hydroxyethyl)-2,3,5,8-tetramethyl-6,7-di(beta-carboxyethyl) porphyrin 3 was perfused; the diglucuronide of the alpha-bilirubin 11 comprised 65% of the excreted bile bilirubins, the monoglucuronide was 25% of the total and the free alpha-bilirubin 11 10% of the total. Perfusion of hematohemin gave 58% of the diglucuronide of alpha-hematobilirubin, as well as 40% of the monoglucuronides, and 2% of the free alpha-hematobilirubin. The simultaneous perfusion of hematohemin and of hemin IX produced an inhibition of the degradation of the hemin IX, while hematohemin was degraded as described above. It was concluded that the normal rat liver is prepared to dispose of exogenously added hemins by their oxidation to alpha-biliverdins, reduction of the latter to the corresponding alpha-bilirubin and excretion of their conjugated derivatives through the bile duct.

Animals↗
PubMed1981

Specificity of heme oxygenase: a study with synthetic hemins.

A large number of synthetic iron porphyrins were enzymatically oxidized by a microsomal heme oxygenase preparation from rat liver. They all had in common two vicinal propionic acid residues at C6 and C7. Iron porphyrins of type I were not substrates of the enzyme. Iron porphyrins that carried electron-withdrawing substituents (acyl residues) at C2 and C4 were substrates of heme oxygenase, although the product yields were reduced. Several iron porphyrins, such as hemin XIII (4) and hem III (5), were better substrates of heme oxygenase than the natural substrate hemin IX (1). The enzymatic oxidation was selective for the alpha-methine bridge, and the alpha-biliverdins obtained were reduced by Biliverdin reductase to the corresponding alpha-bilirubins. Preincubation of the enzymatic system with hemin IX (1) and hemin XIII (4) in the absence of NADPH resulted in an inhibition of their oxidation. The iron-free porphyrins which carried two vicinal propionic acid residues at C6 and C7 were also found to be inhibitors of the enzymatic system when preincubated with the latter. The presence of hematochemin IX (18) suppressed the enzymatic oxidation of hemin IX (1).

Animals↗