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Biomedical subjects

P M Harrison

Publications and source records attributed to P M Harrison.

At least 91 records · Page 5Linked to original sources
PubMed1990

Serial prothrombin time as prognostic indicator in paracetamol induced fulminant hepatic failure.

OBJECTIVE: To find out whether changes in the daily prothrombin time are of prognostic importance in patients with paracetamol induced fulminant hepatic failure. DESIGN: Retrospective study. SETTING: The Liver Unit, King's College Hospital, London. PATIENTS: 150 Consecutive patients with paracetamol induced fulminant hepatic failure admitted between October 1986 and February 1989. MAIN OUTCOME MEASURE: Death. RESULTS: Of the 150 patients, 72 (48%) died. In all, 34 of the 37 (92%) patients with a peak prothrombin time of greater than or equal to 180 seconds died as did 20 of the 41 (49%) with a time of 130-179 seconds, nine of the 25 (36%) with a time of 90-129 seconds, and nine of the 47 (19%) with a time of less than 90 seconds. Of the 42 patients with a continuing rise in prothrombin time between days 3 and 4 after overdose, 39 died (93%) compared with 21 of the 96 (22%) in whom the prothrombin time fell. CONCLUSIONS: These data indicate that a continued increase in prothrombin time on day 4 after overdose and a peak prothrombin time of greater than or equal to 180 seconds identify at an early stage those patients with a less than 8% chance of survival. Liver transplantation should be considered in patients meeting either of these criteria.

Acetaminophen↗
PubMed1990

Improved outcome of paracetamol-induced fulminant hepatic failure by late administration of acetylcysteine.

The influence of acetylcysteine, administered at presentation to hospital, on the subsequent clinical course of 100 patients who developed paracetamol-induced fulminant hepatic failure was analysed retrospectively. Mortality was 37% in patients who received acetylcysteine 10-36 h after the overdose, compared with 58% in patients not given the antidote. In patients given acetylcysteine, progression to grade III/IV coma was significantly less common than in those who did not receive the antidote (51% vs 75%), although the median peak prothrombin time was similar for both groups. Whether the beneficial effect is related to replenishment of glutathione stores or a consequence of another hepatic protective mechanism of acetylcysteine requires further study.

Acetaminophen↗
PubMed1990

Failure of insulin and glucagon infusion to stimulate liver regeneration in fulminant hepatic failure.

A randomised controlled trial of insulin and glucagon infusion was carried out in 18 patients in grade III or IV coma from fulminant hepatic failure due to viral or drug-induced hepatic necrosis to see whether mortality could be reduced by stimulating hepatic regeneration. Nine patients received a continuous infusion of insulin 3 U/h and glucagon 200 micrograms/h made up in 5% dextrose containing 1% human albumin solution (HAS) while controls received 5% dextrose and HAS alone. Baseline plasma insulin and glucagon levels were comparably raised in both groups and, on infusion, rose significantly higher in the insulin- and glucagon-treated patients compared to controls. Two control and one treated patient recovered. Median survival time from enrolment to death was similar for insulin- and glucagon-treated patients and controls--2 and 3 days, respectively. Insulin and glucagon therapy did not enhance hepatic synthetic function, as measured by a fall in prothrombin time or a rise in alpha-fetoprotein; nor did it stimulate hepatic regeneration, only one patient in each group showed histological evidence of hepatic regeneration at post-mortem.

Adult↗
PubMed1989

Identification of the ferroxidase centre in ferritin.

Ferroxidase activity in human H-chain ferritin has been studied with the aid of site-directed mutagenesis. A site discovered by X-ray crystallography has now been identified as the ferroxidase centre. This centre is present only in H-chains and is located within the four-helix bundle of the chain fold.

Animals↗
PubMed1989

Mössbauer spectroscopic study of the initial stages of iron-core formation in horse spleen apoferritin: evidence for both isolated Fe(III) atoms and oxo-bridged Fe(III) dimers as early intermediates.

Ferritin stores iron within a hollow protein shell as a polynuclear Fe(III) hydrous oxide core. Although iron uptake into ferritin has been studied previously, the early stages in the creation of the core need to be clarified. These are dealt with in this paper by using Mössbauer spectroscopy, a technique that enables several types of Fe(II) and Fe(III) to be distinguished. Systematic Mössbauer studies were performed on samples prepared by adding 57Fe(II) atoms to apoferritin as a function of pH (5.6-7.0), n [the number of Fe/molecule (4-480)], and tf (the time the samples were held at room temperature before freezing). The measurements made at 4.1 and 90 K showed that for samples with n less than or equal to 40 at pH greater than or equal to 6.25 all iron was trivalent at tf = 3 min. Four different Fe(III) species were identified: solitary Fe(III) atoms giving relaxation spectra, which can be identified with the species observed before by EPR and UV difference spectroscopy; oxo-bridged dimers giving doublet spectra with large splitting, observed for the first time in ferritin; small Fe(III) clusters giving doublets of smaller splitting and larger antiferromagnetically coupled Fe(III) clusters, similar to those found previously in larger ferritin iron cores, which, for samples with n greater than or equal to 40, gave magnetically split spectra at 4.1 K. Both solitary Fe(III) and dimers diminished with time, suggesting that they are intermediates in the formation of the iron core. Two kinds of divalent iron were distinguished for n = 480, which may correspond to bound and free Fe(II).

Animals↗
PubMed1989

Recombinant H-chain ferritins: effects of changes in the 3-fold channels.

Human H-chain ferritins bearing sequence changes in the 3-fold channels have been expressed in E. coli to investigate the role of these channels in iron-storage processes. The proteins assemble into shells resembling those of native ferritins. Iron uptake measurements indicate that residues in the 3-fold channels are involved neither in initial Fe(II)-oxidation nor in iron-core nucleation.

Amino Acid Sequence↗
PubMed1989

Amino acid sequence of the bacterioferritin (cytochrome b1) of Escherichia coli-K12.

The complete amino acid sequence of bacterioferritin (cytochrome b1) from Escherichia coli-K12 has been derived from the nucleotide sequence of the cloned gene. It comprises 158 amino acid residues giving an Mr of 18,495. The identity of the gene product was confirmed by an 87 residue N-terminal sequence obtained from the purified protein, but it differs significantly from much of the previously published partial amino acid sequence (1). Secondary structure prediction indicates a high alpha-helical content consistent with a 4-helix-bundle conformation. The fully assembled bacterioferritin molecule comprising 24 identical subunits and 12 haem moieties is a tetracosamer with an Mr of approximately 452,000.

Amino Acid Sequence↗
PubMed1989

Molecular size and symmetry of the bacterioferritin of Escherichia coli. X-ray crystallographic characterization of four crystal forms.

X-ray crystallographic data from four crystal forms of Escherichia coli bacterioferritin show that the molecule has a diameter in the range 119 to 128 A. Molecules are composed of 24 subunits arranged in 432 symmetry. In both size and symmetry the molecule resembles ferritin from eukaryotes. The four crystal forms are monoclinic, space group P2(1) with unit cell dimensions a = 118.7 A, b = 211.6 A, c = 123.3 A and beta = 119.1 degrees; orthorhombic, C222(1), a = 128.7 A, b = 197.1 A, c = 202.8 A; tetragonal, P4(2)2(1)2, a = b = 210.6 A, c = 145.0 A and cubic, I432, a = 146.9 A.

Bacterial Proteins↗
PubMed1989

Ferritin subunits in livers of siderotic mice.

The major ferritin species of mouse liver has been resolved by SDS-PAGE into two bands similar to the H and L subunits of rat liver ferritin with the L subunit predominating. Amino acid sequencing has confirmed the major, faster-migrating component as L chain. An additional, electrophoretically fast, minor ferritin was isolated from siderosome-containing subcellular fractions. In denaturing gels it gave a single 'F' subunit band of about 17 kDa, significantly smaller than the L and H subunits (about 20 and 21 kDa respectively). A small fragment isolated from the fast ferritin was sequenced. It corresponds to a 19-residue C-terminal peptide cleaved from L subunits in the assembled molecules. The F subunit must be derived from L subunits by loss of this peptide, and is not the expression product of a different gene. 'Fast' ferritins of siderotic mice and rats are thus analogous.

Amino Acid Sequence↗
PubMed1989

Lysosomal and cytosolic ferritins. A biochemical and electron-spectroscopic study.

Cytosolic and lysosomal ferritin and haemosiderin were isolated from rat livers which had been iron-loaded by four intraperitoneal injections of iron-dextran. The cytosolic and lysosomal ferritins, prepared in a phosphate-free medium, were subjected to gel-filtration chromatography on Sepharose 6B, yielding four fractions: a cytosolic monomeric (CMF) and void-volume ferritin fraction (CVVF), and a lysosomal monomeric (LMF) and void-volume ferritin fraction (LVVF). Of each fraction the following aspects were examined: (a) immunoreactivity against specific antiserum; (b) the Fe/P mass ratio and the effect of dialysis on this ratio using electron probe micro-analysis (EPMA); (c) morphology and Fe-specific imaging using electron spectroscopic imaging (ESI) and electron energy loss spectroscopy (EELS). For haemosiderin one aspect, the Fe/P ratio, was determined before and after extensive purification. The following results were obtained (a) All ferritin fractions reacted with anti- (rat liver ferritin). (b) The Fe/P ratios as determined in CMF in an haemosiderin were not affected by dialysis or extensive purification, respectively. The Fe/P ratio in CVVF was affected by dialysis. In the lysosomal fractions, only a trace of phosphorus (LVVF) or no phosphorus (LMF) was detected. (c) Morphologically, CMF and CVVF were found to be rather homogeneous; the iron core diameters of both fractions were in the known size range.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Release of iron from ferritin molecules and their iron-cores by 3-hydroxypyridinone chelators in vitro.

Ferritin molecules contain 24 subunits forming a shell around an inorganic iron-core. Release of iron(III) from ferritin and its isolated iron-cores by a series of hydroxypyridinone chelators with high affinities for iron(III) has been compared. The results collectively suggest that the chelators act by penetrating the protein shell and interacting directly with the iron-core in ferritin. Iron(III) is probably removed bound to a single ligand, but once outside the protein shell, the trihydroxypyridinone iron(III) complex predominates. The order of effectiveness of a group of pyridinones found for iron removal from ferritin molecules in solution differs from that obtained with hepatocytes in culture or with whole animals, where membrane solubility and other factors may modulate the response.

Animals↗
PubMed1989

Cloning, sequencing, and mapping of the bacterioferritin gene (bfr) of Escherichia coli K-12.

The bacterioferritin (BFR) of Escherichia coli K-12 is an iron-storage hemoprotein, previously identified as cytochrome b1. The bacterioferritin gene (bfr) has been cloned, sequenced, and located in the E. coli linkage map. Initially a gene fusion encoding a BFR-lambda hybrid protein (Mr 21,000) was detected by immunoscreening a lambda gene bank containing Sau3A restriction fragments of E. coli DNA. The bfr gene was mapped to 73 min (the str-spc region) in the physical map of the E. coli chromosome by probing Southern blots of restriction digests of E. coli DNA with a fragment of the bfr gene. The intact bfr gene was then subcloned from the corresponding lambda phage from the gene library of Kohara et al. (Y. Kohara, K. Akiyama, and K. Isono, Cell 50:495-508, 1987). The bfr gene comprises 474 base pairs and 158 amino acid codons (including the start codon), and it encodes a polypeptide having essentially the same size (Mr 18,495) and N-terminal sequence as the purified protein. A potential promoter sequence was detected in the 5' noncoding region, but it was not associated with an "iron box" sequence (i.e., a binding site for the iron-dependent Fur repressor protein). BFR was amplified to 14% of the total protein in a bfr plasmid-containing strain. An additional unidentified gene (gen-64), encoding a relatively basic 64-residue polypeptide and having the same polarity as bfr, was detected upstream of the bfr gene.

Amino Acid Sequence↗
PubMed1988

The identity of Escherichia coli bacterioferritin and cytochrome b1.

Two different procedures were used to prepare pure samples of 'cytochrome b1' (column chromatography) and 'bacterioferritin' (immunoprecipitation) from Escherichia coli K-12 strain CA265. Both were crystallized, and X-ray-crystallographic data were compared with those from the bacterioferritin of E. coli strain W3300 used as a standard. We conclude that 'cytochrome b1' and 'bacterioferritin' are identical.

Bacterial Proteins↗
PubMed1988

Self-assembly of apoferritin from horse spleen after reversible chemical modification with 2,3-dimethylmaleic anhydride.

Apoferritin from horse spleen is composed of 24 subunits that undergo partial dissociation after chemical modification with 2,3-dimethylmaleic anhydride (DMMA), yielding dimeric, trimeric, and tetrameric intermediates, stable at pH 8.5 and 0 degrees C. Deacylation at neutral pH and elevated temperature provides a means to initiate reassembly by appropriate shifts of the solvent conditions. In order to monitor the pathway of self-assembly, starting from different intermediates of dissociation, dimers, trimers, and tetramers were isolated and investigated with respect to their capacity to accomplish reassociation. Intrinsic protein fluorescence, gel permeation chromatography, and analytical ultracentrifugation were applied to characterize the intermediate and final stages of association. The assembly of both the dimer and trimer yields greater than 85% of the native tetracosamer; the overall rate, starting from the dimer, exceeds the one starting from the trimer. Under comparable conditions, the tetramer exhibits only partial reassociation via the dimer and monomer; the corresponding dissociation reaction determines the observed slower rate. Significant assembly intermediates are "structured monomers", dimers, trimers, and dodecamers. Polymerization of the dimer via the tetramer, octamer, etc., does not occur on the pathway of assembly. The results confirm the assembly scheme proposed previously on the basis of cross-linking and spectroscopic experiments [Gerl, M., & Jaenicke, R. (1987) Eur. Biophys. J. 15, 103-109]. Comparison of structural models involving the different subunit interactions responsible for the sequential association supports the monomer----dimer----trimer----hexamer----dodecamer----tetracosamer mechanism of apoferritin self-assembly.

Animals↗