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Biomedical subjects

R N Mullinger

Publications and source records attributed to R N Mullinger.

13 recordsLinked to original sources
PubMed1993

Antecedent insulin level and pattern of induction of acute hypoglycaemia do not affect subsequent counterregulatory responses in healthy subjects.

1. This study was designed to determine whether the duration and pattern of prior insulin exposure modulate the symptomatic and counterregulatory responses to hypoglycaemia. 2. Ten healthy non-obese subjects (five males/five females age 25 +/- 1 years, mean +/- SEM) were made hypoglycaemic in three ways: (i) a hyperinsulinaemic (60 m-units min-1 m-2; plasma insulin concentration 95 m-units/I) clamp, with 1 h of euglycaemia, blood glucose level 4.5 mmol/l, followed by 30 min of hypoglycaemia, at a stable glucose nadir of 2.0 mmol/l (i.e. euglycaemic then hypoglycaemic clamp: E + HC); (ii) an identical hypoglycaemic clamp without preceding hyperinsulinaemic euglycaemia (i.e. a hypoglycaemic clamp: HC); (iii) insulin infusion only, discontinued at a blood glucose level of 3.0 mmol/l (II). Blood glucose level reached the same nadir as on E + HC and HC, and did not fall further. At the glucose nadir, and 15 and 30 min after, the plasma insulin concentration was 23, 7 and 4 m-units/l, respectively, on the II visit. 3. At the glucose nadir, plasma glucagon level, plasma adrenaline level, sweating rate, heart rate, blood pressure, and overall and individual symptom scores (using visual analogue scales) were the same on E + HC, HC and II. 4. There were no significant differences in neurohormonal response between E+HC and HC, but more subjects felt hypoglycaemic on E + HC on arrival at the glucose nadir (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1976

Amino acid sequence of a four-iron-four-sulphur ferredoxin isolated from Bacillus stearothermophilus.

1. The primary structure of a 4Fe-4S ferredoxin from Bacillus stearothermophilus was determined and shown to consist of a single polypeptide chain of 81 amino acid residues. The molecular weight of the holoprotein is about 9120. 2. There are only four cysteine residues in the molecule; three of these are located near the N-terminus as a Cys-X-X-Cys-X-X-Cys segment, and the fourth cysteine residue is followed by a proline and located in the C-terminal half. 3. The Fe-S chromophore in B. stearothermophilus ferredoxin was previously well characterized and was shown to consist of a single 4Fe-4S cluster. This ferredoxin sequence establishes for the first time the relative location of the four cysteine residues necessary to bind the 4Fe-4S cluster of a 4Fe ferredoxin, and is in agreement with the criteria for the relative positions of the cysteines proposed from X-ray-crystallographic studies on an 8Fe (two 4Fe-4S clusters) ferredoxin. 4. The sequence of B. stearothermophilus ferredoxin is homologous in many segments to that of other bacterial ferredoxins, the degree of homology being greater towards ferredoxins from Desulfovibrio gigas and photosynthetic bacteria than to Clostridial ferredoxins. 5. The presence of a relatively higher number of glutamic acid and lower number of cysteine residues in the molecule may explain the greater thermal stability and oxygen-insenstivity of this ferredoxin.

Amino Acid Sequence↗
PubMed1975

Physicochemical characterization of the four-iron-four-sulphide ferredoxin from Bacillus stearothermophilus.

1. A stable ferredoxin was prepared from Bacillus stearothermophilus and purified by chromatography on DEAE-cellulose and by electrophoresis. 2. The minimum molecular weight determined from the amino acid composition was about 7900 and this was in reasonable agreement with a value of 8500 determined by polyacrylamide-gel electrophoresis. The ferredoxin contained four iron atoms and four labile sulphide groups per molecule. 3. The optical absorption, optical-rotatory-dispersion and circular-dichroism spectra are typical of ferredoxins containing 4Fe-4S clusters. 4. Oxidation-reduction titrations, combined with electron-paramagnetic-resonance (e.p.r.) spectroscopy, showed that the protein has a mid-point potential, at pH8, of -280 +/- 10mV, and that only one electron-accepting paramagnetic species is present. 5. The e.p.r. spectrum of the reduced ferredoxin is more readily saturated with microwave power at low temperatures than those of the eight-iron ferredoxins, indicating that there is another mechanism of electron-spin relaxation in the latter. 6. Mossbauer spectra of both redox states were observed over a range of temperatures and in magnetic fields. At high temperatures (77 degrees K and above) both redox states appear as quadrupole-split doublets; in the reduced state two resolved doublets are seen, suggesting appreciable localization of the additional reducing electron. 7. The average chemical shift indicates formal valences of two Fe3+ and two Fe2+ in the oxidized state and three Fe2+ and one Fe3+ in the reduced state. However, the spectra indicate that there are differing degrees of electron delocalization over the iron atoms. 8. At low temperatures (4.2 degrees K) the oxidized form shows no hyperfine magnetic interaction, even in an applied magnetic field, evidence that the oxidized ferredoxin is in a non-magnetic state as a result of antiferromagnetic coupling between the iron atoms. 9. At 4.2 degrees K the reduced form shows a broad asymmetric pattern resulting from magnetic hyperfine interaction. This contrasts with the reduced ferredoxin of Clostridium pasteurianum, which shows a doublet, suggesting that in the latter there may be interaction between the two 4Fe-4S centres. 10. In large applied magnetic fields, positive and negative hyperfine fields are seen in the Mossbauer spectra of the reduced ferredoxin, evidence for antiferromagnetic coupling between the iron atoms in the 4Fe-4S centre. The high-field spectra of the reduced ferredoxin of B. stearothermophilus are similar to those of the reduced ferredoxin of C. pasteurianum.

Amino Acids↗
PubMed1969

Properties of heparan sulphate and chondroitin sulphate from young and old human aortae.

1. Glycosaminoglycans were liberated from old and young human ascending aortae by digestion with papain. Heparan sulphate and chondroitin sulphate were separated by the different solubilities of their complexes with cetylpyridinium chloride in solutions of sodium chloride. Final fractionation was achieved by salt-gradient column chromatography on Dowex 1 (Cl(-)form). 2. Heparan sulphate from old aortae showed a slight, but consistent, increase in sulphation compared with heparan sulphate from young aortae. 3. The major amino acids associated with aortic heparan sulphate and chondroitin sulphate were serine, glycine, glutamic acid and aspartic acid. Heparan sulphate and chondroitin sulphate from old aortae contained about twice as much total amino acid as heparan sulphate and chondroitin sulphate from young aortae. Alkali hydrolysis resulted in the destruction of more serine in chondroitin sulphate from old, compared with young, aortae. 4. Molecular weights of glycosaminoglycans from old and young aortae were found to be similar, and in the region of 35000. 5. It is suggested that there is an increased degree of protein-glycosaminoglycan cross-linking in old aortae.

Adolescent↗