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Biomedical subjects

A Treffry

Publications and source records attributed to A Treffry.

51 records · Page 3Linked to original sources
PubMed1984

Ferritin: design and formation of an iron-storage molecule.

Although essential for most forms of life, too much iron is harmful. To cope with these antagonistic phenomena an iron-storage molecule, ferritin, has evolved. The structure of horse spleen apoferritin, which has recently been refined, consists of 24 symmetrically related subunits forming a near-spherical hollow shell. In ferritin the central cavity is occupied by an iron core of 'ferrihydrite', a geologically ephemeral mineral found in hot or cold springs and in mine workings, or produced in the laboratory by heating solutions of ferric salts. Ferritin itself forms most readily from apoferritin, in the presence of dioxygen, from FeII, not FeIII. Access to its interior is through small intersubunit channels, and the protein influences both the rate of FeII-oxidation and the form of oxide produced.

Animals↗
PubMed1984

The effect of iron on ferritin turnover in rat liver.

It has previously been reported that in rat liver the rates of synthesis and degradation of ferritin labelled with [14C]leucine or arginine are dependent on the iron status of the rats. It has also been concluded that isoferritins differ markedly in their rates of turnover. Here we provide experimental evidence which shows that the rate of degradation of rat liver ferritin (labelled by injection of [14C]bicarbonate to minimise problems of reutilisation) is unaltered by repeated iron injection, although ferritin synthesis is stimulated. Our data also strongly suggest that the proposed differential degradation of isoferritins is improbable.

Animals↗
PubMed1984

Spectroscopic studies on the binding of iron, terbium, and zinc by apoferritin.

Ultraviolet difference spectroscopy has been used to study Fe (III)-apoferritin complexes formed after addition of Fe (II) to apoferritin in air. At constant iron, the recorded spectra varied with time after Fe (II) addition and with the number of iron atoms/molecule (protein concentration). The results indicate that after production of an initial complex, rearrangement or migration of Fe (III) atoms occurs, with polynuclear species forming as end-product, probably by hydrolytic polymerization. The presence of Tb3+ or Zn2+ ions affected the Fe (III) spectra and their development in different ways. The combined data suggest that more than one site, or processes, are involved in ferritin iron-core formation and that some of the metal sites are clustered.

Animals↗
PubMed1983

Effect of ferritin-containing fractions with different iron loading on lipid peroxidation.

Ferritin-containing fractions with different degrees of iron loading were prepared. All ferritin fractions stimulated the peroxidation of bovine brain phospholipid liposomes, as measured by the formation of thiobarbituric acid-reactive material. This stimulation was increased in the presence of ascorbate. Iron salts of equivalent concentration to those of the ferritin fractions were more stimulatory to lipid peroxidation at the higher iron concentrations. None of the fractions inhibited ascorbate-dependent peroxidation in the presence of added iron salts.

Ascorbic Acid↗
PubMed1980

Evidence for post-translational changes in rat liver ferritin.

Analysis of rat liver isoferritins labelled by NaH14CO3 injection shows that acidic isoferritins decay exponentially, while activity in more basic isoferritins rises over 2-3 days. This suggests that isoferritins of low pI become more basic by post-translational modification, occurring over the whole life time of the protein.

Animals↗
PubMed1979

The binding of ferric iron by ferritin.

Equilibrium-dialysis experiments with 59Fe-labelled Fe(III) chelate solutions show that ferritin is capable of binding a limited number of Fe(III) atoms. Some of this Fe(III) is readily removed, but up to about 200 Fe(III) atoms/molecule remain bound after extensive washing. Some exchange of labelled Fe(III) with endogenous unlabelled ferritin Fe occurs during prolonged dialysis against 59Fe(III)-citrate, but there is a net binding of Fe(III). Bound Fe(III) resembles endogenous Fe(III) in several respects. It appears to be attached to the micelle and not to the protein component of ferritin. Although the physiological mechanism of Fe incorporation into ferritin is unknown, our experiments suggest the possibility that some iron finds its way into ferritin as Fe(III) chelate.

Apoferritins↗
PubMed1974

A study of the reaction of protoporphyrin IX with human globin.

The present paper reports an investigation of the reaction of protoporphyrin IX with globin prepared from the HbA(0) component of human blood. The porphyringlobin produced is always heterogeneous; however, when globin is used immediately after preparation, its affinity for porphyrin is higher and the product less heterogeneous than when the globin has been frozen or freeze-dried. The affinity of globin for haemin is less affected by its history. With freshly prepared globin, reconstitution at room temperature provides a different distribution of porphyringlobin species than reconstitution at 4 degrees C. Further changes in the species distribution of cold-reconstituted samples may be observed by gel electrophoresis when the samples are aged for 24h at room temperature. Chromatographic separation of such porphyringlobin samples on CM-Sephadex generally revealed five species with two in predominating amounts. It was consistently observed that over a period of 18 days, the faster moving of the two main components decreased in amount whereas the slower-moving component correspondingly increased. However, when the main components are separated, they remain homogeneous over the same length of time. The effect of light on porphyringlobin was also investigated. It was shown that porphyringlobin is photo-oxidized: as a result the porphyrin is destroyed together with most of the histidine, methionine and all of the tryptophan residues of the protein.

Amino Acids↗
PubMed1974

A study of the properties of two porphyringlobin species formed in the reaction of protoporphyrin IX with human globin.

Globin was prepared from the main (A(0)) component of human haemoglobin and reacted with protoporphyrin IX; the product, when subjected to chromatography on CM-Sephadex, separated into fast- and slow-moving species. These were isolated for examination. The dissociation constant for the tetramer-dimer equilibrium of fast-moving porphyringlobin was determined at 2.8x10(-6)m; this is to be compared with values of 2.2x10(-6)m and 8x10(-8)m determined for oxyhaemoglobin and the slow-moving porphyringlobin respectively. It was also shown that the thiol groups of fast-moving porphyringlobin react with 4,4'dithiodipyridine at an identical rate with those of oxyhaemoglobin; in comparison, the rates of reaction of deoxyhaemoglobin and porphyringlobin are much slower but are again identical with one another. The quenching of porphyringlobin fluorescence by I(-) ions was also studied. The quenching could not be represented by a simple Stern-Volmer relationship (whereas that of porphyrin-apomyoglobin is), but was represented by a model in which the fluorescence of fast-moving porphyringlobin was more accessible to the quencher than that of the slow-moving component. Similarly, fast-moving porphyringlobin was photodecomposed more rapidly by oxygen than the slow-moving species.

Binding Sites↗
PubMed1974

A study of the properties of hybrids of oxyhaemoglobin and deoxyhaemoglobin with two porphyringlobin species.

The fluorescence of porphyringlobin is quenched on adding haemoglobin to its solutions. It is suggested that this result indicates the formation of hybrids (comprising a dimer of porphyringlobin and a dimer of haemoglobin) in which quenching occurs by energy transfer from the porphyrin to the haem groups of the protein. From an analysis of fluorescence quenching, dissociation constants were calculated for the hybrids of oxy- and deoxyhaemoglobin with the fast- and slow-moving porphyringlobin species isolated by chromatography on CM-Sephadex (Treffry & Ainsworth, 1974). The values obtained are: deoxyhaemoglobin-fast-moving porphyringlobin, 0.8x10(-9)m; deoxyhaemoglobin-slow-moving porphyringlobin, 5x10(-10)m; oxyhaemoglobin-fast-moving porphyringlobin, 0.8x10(-6)m; oxyhaemoglobin-slow-moving porphyringlobin, 1.2x10(-7)m. The rates of reactions of solutions of haemoglobin and porphyringlobin, containing hybrids, with the thiol reagent 4,4'-dithiodipyridine showed that the thiol groups of the hybrids deoxyhaemoglobin-fast-moving porphyringlobin and oxyhaemoglobin-slow-moving porphyringlobin react more slowly than expected on the basis of composition alone: this result indicates that the deoxy and slow-moving conformations are the more stable, imposing themselves partially on to the fast-moving or oxy dimer of the hybrid. Also the rate of the reaction of CO with deoxyhaemoglobin is decreased when slow-moving porphyringlobin is added to its solutions: this is reflected in a movement of the oxygen equilibrium curve of such a mixture to higher oxygen partial pressures. Similar experiments with deoxyhaemoglobin solutions containing fast-moving porphyringlobin, showed an initial increase in the rate of CO uptake. Correspondingly, the oxygen equilibrium curve of the mixture showed an increased affinity for oxygen. Approximate calculations to determine the oxygen equilibria of the hybrids indicate that a functional dimer retains co-operative characteristics even when the dimer accompanying it within the tetramer has the reacted conformation.

Animals↗