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Biomedical subjects

Y Ilan

Publications and source records attributed to Y Ilan.

143 records · Page 8Linked to original sources
PubMed1980

Chain inequivalence in bovine methemoglobin.

Using pulse radiolysis, a single heme in the tetramer of bovine methemoglobin was reduced within a few microseconds to the ferro state, producing a valence intermediate. The kinetics of oxygen binding to the valence intermediate as well as the re-oxidation of the ferro-heme to the ferric state were studied as a function of pH. The kinetics of the oxygenation revealed the existence of two species, characterized by high and low affinities for oxygen that are associated with two quaternary structures (R and T, respectively). A sigmoidal curve representing a transition between the two states as a function of pH was derived. Above pH 7.7 only the R state could be observed, while below pH 6.5 the T state was dominant. The reaction between the valence intermediate and ferricyanide at pH 7.75 (R state) consisted of two (about) equal contributions (k1 = 23 x 10(4) M-1 S-1; k2 = 2.1 x 10(4) M-1 S-1) attributed to the beta and alpha subunits within the tetramer, respectively. At pH 6.3 (T state) a similar phenomenon was observed (k1 = 69 x 10(4) M-1 S-1; k2 = 3.7 x 10(4) M-1 S-1), indicating chain inequivalences both in the T and the R states of methemoglobin. In the presence of inositol hexakisphosphate the T leads to R transition, as monitored by oxygenation of the valence intermediate, was shifted up to a higher pH by about 0.35. Yet similar rate constants exhibiting similar chain inequivalences have been measured.

Animals↗
PubMed1979

Partitioning of electrostatic and conformational contributions in the redox reactions of modified cytochromes c.

The reduction of acetylated, fully succinylated and dicarboxymethyl horse cytochromes c by the radicals CH3CH(OH), CO2.-, O2.-, and e-aq' and the oxidation of the reduced cytochrome c derivatives by Fe(CN)3-6 were studied using the pulse radiolysis technique. Many of the reactions were also examined as a function of ionic strength. By obtaining rate constants for the reactions of differently charged small molecules redox agents with the differently charged cytochrome c derivatives at both zero ionic strength and infinite ionic strength, electrostatic and conformational contributions to the electron transfer mechanism were effectively partioned from each other in some cases. In regard to cytochrome c electron transfer mechanism, the results, especially those for which conformational influences predominate, are supportive of the electron being transferred in the heme edge region.

Acetylation↗
PubMed1979

Intramolecular electron transfer and binding constants in iron hexacyanide-cytochrome c complexes as studied by pulse radiolysis.

Internal oxidation and reduction rates of horse cytochrome c in the complexes CII . Fe(III)(CN)6(3)- and CIII . Fe(II)(CN)6(4)-, are 4.6 . 10(4)s-1 and 3.3 . 10(2)s-1, respectively. The binding site of the iron hexacyanide ions on either CII or CIII are kinetically almost indistinguishable; binding constants range from 0.87 . 10(3) to 2 . 10(3)M-1. The present pulse radiolytic kinetic data is compared with that from NMR, T-jump and equilibrium dialysis studies.

Animals↗
PubMed1978

Do copper ions influence the reduction of ferricytochrome C by O-2?

Recently, it was suggested that the measured rate of reduction of ferricytochrome C by O-2 below pH 8, was too high in the presence of high concentrations of formate (Koppenol, W.H., Van Buuren, K.J.H., Butler J. and Braams, R. (1976) Biochim. Biophys. Acta 449, 157-168). The high values were attributed to the presence of impurities of copper, which compete for O-2. This assumption is consistent with either a decrease in the reduction yield of ferricytochrome C in the presence of copper, or with a very fast reaction of Cu(I) with ferricytochrome C. It was previously shown by us and by others that the reduction yield of ferricytochrome C by O-2 IS 100%. We measured the rate of reduction of ferricytochrome C by Cu(I), and found that this reaction is slow: k = (1.5 +/- 0.5) . 10(3) M-1 . s-1. Therefore, our results rule out the possibility that below pH 8 copper impurities affect the measured rate constant of the reduction of ferricytochrome C by O-2.

Copper↗
PubMed1977

H/2H isotope effect in redox reactions of cytochrome c.

The rate of reaction of ferro- and ferricytochrome c (C(II) and C(III) with ferri- and ferrocyanide and of C(III) with 02- and CO2- was determined in H2O and in 2H2O in the temperature range 5-35 degrees C. No isotope effect was evident in any of the reductions of C(III); the apparent energy of activation was identical in H2O and 2H2O. An isotope effect with kH2O/k2H2O = 1.25 to 1.85, depending on pH for instance was observed in the oxidation of C(II), in the slow phase of oxidation which involves conformational changes. An interpretation (supported by evidence from previous work) involving water molecules in the close vicinity of the reaction site on the protein is discussed.

Carbon Dioxide↗
PubMed1976

Reactions of the ferri-ferrocytochrome-c system with superoxide/oxygen and CO2-/CO2 studied by fast pulse radiolysis.

The reduction of ferricytochrome c by O2- and CO2- was studied in the pH range 6.6-9.2 and Arrhenius as well as Eyring parameters were derived from the rate constants and their temperature dependence. Ionic effects on the rate indicate that the redox process proceeds through a multiply-positively charged interaction site on cytochrome c. It is shown that the reaction with O2- (and correspondingly with O2 of ferrocytochrome c) is by a factor of approx. 10(3) slower than warranted by factors such as redox potential. Evidence is adduced to support the view that this slowness is connected with the role of water in the interaction between O2-/O2 and ferri-ferrocytochrome c in the positively charged interaction site on cytochrome c in which water molecules are specifically involved in maintaining the local structure of cytochrome c and participate in the process of electron equivalent transfer.

Binding Sites↗
PubMed1976

The study of 1-electron equivalent oxidation-reduction reactions by fast pulse generation of reagents. Cytochrome c/ferri-ferrocyanide system.

The method of pulse radiolysis was used to generate reagents in situ in times (500 ns to 1.5 mus) short compared with the rates of the observed biochemical processes. This "instant" mixing technique is compared with rapid stopped flow measurements (limited in rates and concentrations) and T-jump measurements (limited to relaxation in the neighborhood of equilibrium) for the ferro-ferricytochrome c (C(II)-C(III))/ferro-ferricyanide (FCN(II)-FCN(III)) system. The reagents generated in situ were C(II) or FCN(III). Kinetically indistinguishable binding sites exist on C(II) and C(III) for hexacyanide anions. Reductive electron transfer to the protein proceeds within the FCN(II)-C(III) complex, with a rate of 400 s-1. The binding of FCN(II) on C(II) slows down the oxidation of C(II) by FCN(III). The sites of interaction on C(II) or C(III) with FCN(III) show effective charges of approximately +2. The association constant per binding site derived from the kinetics of electron transfer is greater than or equal to 10(4) M-1 for FCN(II)-C(II) and less than or equal to 10(4) M-1 for FCN(III)-C(III). Specific clusters of amino acids in the model of cytochrome C are suggested as binding sites. The oxidation-reduction reactions of FCN appear to involve electron equivalent transfer to and from such somewhat remote binding sites on the protein. Anions such as phosphate or sulphate also bind to these, less strongly than hexacyanides. In the presence of perchlorate the kinetics show the resolution of the pK=9.3 of C(III) into two parts: (a) optical changes at 695 nm due to ligand interchange on the heme-iron, unaffected by perchlorate and (b), a kinetic change leading to biphasic oxidation of C(II), with pK=7.4. This is attributed to the effect of perchlorate on water structure in the close environment of the binding sites. The high rate of oxidation of relaxed C(II) by FCN(III), (2 X 10(8) M-1 S-1 at mu=0) is not in agreement with an outer sphere Marcus mechanism. Nonrelaxed C(II) having a structure closer to C(III) transfers electron to FCN(III) even faster (k=3 X 10(9) M-1 S-1 at mu=0).

Anions↗
PubMedDate not supplied

Impaired liver function tests in patients treated with antithymocyte globulin: implication for liver transplantation.

Antithymocyte globulin (ATG) is traditionally used as a conventional immunosuppression agent in various pathological states including severe aplastic anaemia (SAA), graft versus host disease (GVHD), and for the prevention and treatment of graft rejection and GVHD post bone marrow and liver transplantation. We reviewed the liver functions of 16 haematological patients with no previous liver disorders who received ATG as part of their pre-bone marrow transplantation (BMT) conditioning regimen, and the liver function tests of five SAA patients who received ATG as part of their treatment. Liver functions were evaluated at day -1 pre-, and days +3 and +10 post-ATG treatment. All patients had normal liver functions before treatment. In the haematological patients, the mean serum lactic dehydrogenase (LDH) levels increased from 408.7 +/- 37.7 U/l pre-treatment to 1394.4 +/- 488.7 U/l 3 days post-treatment (n = 16; p < 0.029), and then declined to 561.4 +/- 61.3 U/l 10 days post-treatment (n = 16; p < 0.043). The mean alanine aminotransferase (ALT) levels increased from 51.9 +/- 11.3 U to 184.6 +/- 74.6 U (n = 16; p < 0.036), and then declined to 121.9 +/- 61.3 U (n = 16; NS). The mean aspartate amino transferase (AST) levels increased from 31.2 + 5.7 U to 152.0 +/- 67.0 U (n = 16; p < 0.44) and then declined to 46.0 +/- 14 (n = 16; p < 0.049). The mean tau-glutamyltransferase (GTP) levels increased from 93.0 +/- 34 to 188.0 +/- 36 (n = 16; p < 0.02), and were 168.0 +/- 37.0 at day +10 (n = 16; NS). The mean bilirubin levels increased from 18.0 +/- 1.9 microM l(-1) to 22.7 +/- 2.8 (n = 16); NS), at day +3 and to 31.9 +/- 6.9 at day +10 (n = 16; NS). In contrast, no significant changes in liver function tests were demonstrated in the SAA patients treated with ATG. The possible pathophysiologic mechanisms and the clinical implications for liver transplantation are discussed.

Adolescent↗
PubMedDate not supplied

Familial cluster of fulminant hepatitis A infection.

Hepatitis A virus is a common cause of a self-limited liver disease. Fulminant hepatitis is a rare complication of acute hepatitis A infection. We report a small epidemic of three consecutive fulminant hepatitis A infections in three previously healthy siblings. This is the first report of a cluster of fulminant hepatitis A.

Acute Disease↗
PubMedDate not supplied

Gastrointestinal involvement in homocystinuria.

Homocystinuria is frequently associated with severe multisystem involvement such as dislocated lenses, skeletal deformities, mental retardation and premature vascular occlusions. Surprisingly, gastro-intestinal involvement has not been described in this disorder. We present a 17 year old boy with homocystinuria due to cystathionine beta-synthase deficiency, who developed severe gastrointestinal involvement, manifested by chronic diarrhoea and acute pancreatitis. The diarrhoea was successfully treated with betaine. Possible pathophysiological mechanisms and suggested treatment are described.

Adolescent↗
PubMedDate not supplied

Elevated growth hormone levels in patients with non-alcoholic chronic liver disease.

High serum concentrations of growth hormone (GH) were found in five patients with chronic liver diseases, including auto-immune chronic active hepatitis (two cases), Budd-Chiari syndrome, primary biliary cirrhosis and hepatitis B virus associated cirrhosis. Mean levels of GH were 27.8 units (normal up to 5). In three patients elevated prolactin levels were also found (mean 37.3 units for two females, normal up to 20), and 36 units in one male (normal up to 9). No other endocrine disorders were found. Although the association of raised GH levels in patients with alcoholic cirrhosis is well known, its occurrence in patients with non-alcoholic chronic liver disease is not fully established. We describe the effect of the disease course, and steroid treatment on GH levels in one patient with auto-immune chronic active hepatitis, and propose possible mechanisms for this elevation.

Adolescent↗
PubMedDate not supplied

Variable efficacy of interferon-alpha treatment on growth of human hepatoma cell lines in vitro.

Three human hepatoma cell lines, PLC/PRF/5, Mahlavu and Sk-Hep 1, two of which contain integrated HBV DNA, were grown in culture and treated with human alpha-IFN for up to 14 days. IFN treatment caused a varying suppression of cell growth of the three hepatoma cell lines. While doubling time and cloning efficiency were significantly reduced for all three hepatoma cell lines tested, 3[H]thymidine incorporation was markedly suppressed, in a dose-dependent fashion, only in treated PLC/PRF/5 cells but not in Sk-Hep 1 and Mahlavu cells. The inhibiting effect of interferon treatment on growth of PLC/PRF/5 cells in vitro was neutralized by antibodies to human IFN. IFN treatment caused a significant suppression of HBsAg and alpha FP secretion by PLC/PRF/5 hepatoma cells. This effect, while constant throughout the observation period for HBsAg, was cumulative for alpha FP secretion. Following discontinuation of treatment, suppression of PLC/PRF/5 hepatoma cell growth was rapidly reversed, and HBsAg and alpha FP secretion returned to their pretreatment levels. These experiments suggest that human alpha-IFN suppresses the growth of some human hepatoma cells in culture but that this effect is dependent on the continuous presence of IFN in the growth medium. Finally, the inhibitory effects of IFN on cell growth differed for the various hepatoma cell lines tested.

Animals↗