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Biomedical subjects

M C Evans

Publications and source records attributed to M C Evans.

At least 145 records · Page 8Linked to original sources
PubMed1975

Region-specific immunoassays for parathyroid hormone.

Immunoassays specific for limited regions of bovine parathyroid hormone were developed in four ways. With the heterogeneous antisera produced by immunizing with intact bovine parathyroid hormone (BPTH 1-84), the specificity of radioimmunoassays could be enhanced by presaturating either with an amino-terminal (BPTH 1-34) or carboxy-terminal (BPTH 53-84) fragment. Then, the antibodies which had not been neutralized reacted exclusively with the opposite end of the molecule, even using [125I]BPTH 1-84 as tracer. With some antisera, the appropriate fragment and intact hormone reacted identically. However, with other antisera, the fragment reacted less well than the intact hormone, possibly because these antisera contain antibodies reacting with the middle of the molcule. Using the labelled fragment ([125I]BPTH 1-34) as tracer, with heterogeneous antisera, radioimmunoassays specific for the amino-terminal region were obtained. With one antiserum, BPTH 1.34 reached identically with the intact hormone, but with another antiserum, the fragment was more reactive than the intact molecule. A region-specific radioimmunoassay was also developed using antibodies produced by immunization with a fragment of the hormone. An antiserum raised against BPTH 1-34 had high affinity for the amino-terminal fragement, but reacted less well with the intact hormone. Immunoradiometric assays, specific for the amino- or carboxy-terminal regions, developed by using immunoadsorbents consisting of a fragment (either BPTH 1-34 or BPTH 53-84) coupled to cellulose. These were used to fractionate 125I-labelled antibodies. With some of these selected antibodies, the appropriate fragment was of lower reactivity than the intact hormone. This may have been due to the presence of an incomplete antigenic site on the fragment, or to conformational differences between the fragment and the corresponding region of the intact hormone. With other selected antibodies the fragment and the intact molecule reacted identically. Careful selection of antisera and of technique is necessary to obtain an assay in which a fragment and the intact hormone behave identically.

Animals↗
PubMed1974

The detection and characterization by electron-paramagnetic-resonance spectroscopy of iron-sulphur proteins and other electron-transport components in chromatophores from the purple bacterium Chromatium.

Low-temperature e.p.r. (electron-paramagnetic-resonance) spectroscopy was used to detect electron-transport components in Chromatium chromatophores with e.p.r. signals in the g=2.00 region. High-potential iron protein (E(m8.0)=+325mV, where E(m8.0) is the midpoint potential at pH8) and a second component (g=1.90, E(m8.0)=+285mV) are oxidized in illuminated chromatophores. Two iron-sulphur proteins (g=1.94) with E(m8.0)=-290mV and E(m8.0)=-50mV are present. One (E(m8.0)=-50mV) is reduced on illumination. A component (g=1.82) with E(m8.0)=-135mV is photoreduced at 10 degrees K. The midpoint potential of this component is altered by o-phenanthroline and pH. The properties of this component suggest that it is the primary electron acceptor of a photochemical system. Another component (g=1.98) also has some of the properties of a primary electron acceptor, but its function cannot be completely defined. These results show that iron-sulphur proteins are present in the electron-transport system of Chromatium and indicate their role in electron transport.

Bacterial Chromatophores↗
PubMed1974

Mössbauer effect in the high-potential iron-sulphur protein from Chromatium. Evidence for the state of the iron atoms.

1. The previous Mössbauer work on Chromatium high-potential iron-sulphur protein by Moss et al. (1968) and Evans et al. (1970) was extended to high applied magnetic fields. 2. Measurements of the reduced protein confirm that it is non-magnetic. 3. Spectra of the oxidized protein in applied magnetic fields clearly indicate that some iron atoms have a positive hyperfine field, which is evidence for antiferromagnetic coupling. 4. The spectra can be interpreted in terms of two types of iron atom with positive and negative hyperfine fields of 9 and 12T respectively. 5. A consideration of the chemical shifts and other evidence suggests formal valences of two Fe(3+) and two Fe(2+) atoms in the non-magnetic reduced state, and three Fe(3+) atoms and one Fe(2+) atom in the oxidized state. 6. However, no separate Fe(3+) and Fe(2+) spectra are seen, suggesting that the d electrons are not localized on particular iron atoms.

Bacterial Proteins↗
PubMed1972

Mössbauer effect in rubredoxin. Determination of the hyperfine field of the iron in a simple iron-sulphur protein.

1. Rubredoxin isolated from the green photosynthetic bacterium Chloropseudomonas ethylica was similar in composition to those from anaerobic fermentative bacteria. Amino acid analysis indicated a minimum molecular weight of 6352 with one iron atom per molecule. 2. The circular-dichroism and electron-paramagnetic-resonance spectra of Ch. ethylica rubredoxin showed many similarities to those of Clostridium pasteurianum, but suggested that there may be subtle differences in the protein conformation about the iron atom. 3. Mössbauer-effect measurements on rubredoxin from Cl. pasteurianum and Ch. ethylica showed that in the oxidized state the iron (high-spin Fe(3+)) has a hyperfine field of 370+/-3kG, whereas in the reduced state (high-spin Fe(2+)) the hyperfine field tensor is anisotropic with a component perpendicular to the symmetry axis of the ion of about -200kG. For the reduced protein the sign of the electric-field gradient is negative, i.e. the ground state of the Fe(2+) is a [unk] orbital. There is a large non-cubic ligand-field splitting (Delta/k=900 degrees K), and a small spin-orbit splitting (D~+4.4cm(-1)) of the Fe(2+) levels. 4. The contributions of core polarization to the hyperfine field in the Fe(3+) and Fe(2+) ions are estimated to be -370 and -300kG respectively. 5. The significance of these results in interpretation of the Mössbauer spectra of other iron-sulphur proteins is discussed.

Amino Acid Sequence↗