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Biomedical subjects

R Blackmore

Publications and source records attributed to R Blackmore.

8 recordsLinked to original sources
PubMed1999

A mutation that improves soluble recombinant hemoglobin accumulation in Escherichia coli in heme excess.

High-level expression of soluble recombinant human hemoglobin (rHb) in Escherichia coli was obtained with several hemoglobin variants. Under identical conditions, two rHbs containing the Presbyterian mutation (Asn-108-->Lys) in beta-globin accumulated to approximately twofold less soluble globin than rHbs containing the corresponding wild-type beta-globin subunit accumulated. The beta-globin Providence(asp) mutation (Lys-82-->Asp) significantly improved soluble rHb accumulation compared to the wild-type beta-globin subunit and restored soluble accumulation of rHbs containing the Presbyterian mutation to wild-type levels. The Providenceasp substitution introduced a negatively charged residue into the normally cationic 2,3-bisphosphoglycerate binding pocket, potentially reducing the electrostatic repulsion in the absence of the polyanion. The average soluble globin accumulation when there was coexpression of di-alpha-globin and beta-Lys-82-->Asp-globin (rHb9.1) and heme was present in at least a threefold molar excess was 36% +/- 3% of the soluble cell protein in E. coli. The average total accumulation (soluble globin plus insoluble globin) was 56% +/- 7% of the soluble cell protein. Fermentations yielded 6.0 +/- 0. 3 g of soluble rHb9.1 per liter 16 h after induction and 6.4 +/- 0.2 g/liter 24 h after induction. The average total globin yield was 9.4 g/liter 16 h after induction. High-level accumulation of soluble rHb in E. coli depends on culture conditions, the protein sequence, and the molar ratio of the heme cofactor added.

Escherichia coli↗
PubMed1997

Incorporation of norvaline at leucine positions in recombinant human hemoglobin expressed in Escherichia coli.

We report here a novel finding that norvaline can be incorporated in place of leucine in recombinant human hemoglobin expressed in Escherichia coli. The presence of the norvaline was confirmed by several analytical methods such as amino acid analysis, peptide mapping, electrospray mass spectrometry, and Edman protein sequencing. It appears that substitution is distributed across both the beta- and di-alpha-globins in purified recombinant hemoglobin. The level of misincorporation correlated with the ratio of the free norvaline/leucine pool available in the cell culture. This suggests that the incorporation of norvaline for leucine occurs through misaminoacylation of tRNALeu, similar to the misincorporation of norleucine for methionine found in many recombinant proteins expressed in E. coli.

Amino Acid Sequence↗
PubMed1997

Stabilization of apoglobin by low temperature increases yield of soluble recombinant hemoglobin in Escherichia coli.

Accumulation of soluble recombinant hemoglobin (rHb1.1) in Escherichia coli requires proper protein folding, prosthetic group (heme) addition, and subunit assembly. This served as a new model system for the study of the effects of temperature, protein synthesis rates, and protein accumulation rates on protein solubility in E. coli. Fermentation expression of rHb1.1 at 30 degrees C from cultures containing a medium or high globin gene dosage (pBR-based or pUC-based plasmids with rHb1.1 genes under the control of the tac promoter) was compared. A medium gene dosage resulted in rHb1.1 accumulating to approximately 7% of the soluble cell protein, of which 78% was soluble. A high globin gene dosage resulted in a > or = 3-fold increase in total globin to 23 to 24% of the soluble cell protein, but 70% was insoluble. Accumulation of insoluble rHb1.1 began immediately upon induction. The proportion of rHb1.1 from the high globin gene dosage that accumulated as insoluble globin was affected by reducing (i) the inducer concentration and (ii) the temperature. Reducing the inducer concentration reduced globin synthesis up to eightfold but increased the proportion of soluble rHb1.1 to 93%. In contrast, total globin protein synthesis was barely affected by reducing the temperature from 30 to 26 degrees C, while soluble globin accumulation increased > 2-fold to approximately 15% of the soluble cell protein. The contrast between the effects of reducing rates of protein synthesis and accumulation and those of reducing temperature suggests that lower temperature stabilizes one or more folding intermediates. We propose a simplified physical model which integrates protein synthesis, folding, and heme association. This model shows that temperature-dependent apoglobin stability is the most critical factor in soluble rHb1.1 accumulation.

Apoproteins↗
PubMed1992

Bacterial nitrite-reducing enzymes.

The enzymic reduction of nitrite takes place in a wide range of bacteria and is found to occur in denitrifying, assimilatory and dissimilatory pathways. In this review we describe the major molecular characteristics of the various enzymes employed in each of these processes.

Bacteria↗
PubMed1986

The purification and some equilibrium properties of the nitrite reductase of the bacterium Wolinella succinogenes.

The bacterium Wolinella succinogenes produces a nitrite reductase enzyme that can be purified to homogeneity in high yield by a combination of detergent extraction, hydroxyapatite chromatography and Mr fractionation. Nitrite reductase activity is found to be present in both a high- and a low-Mr fraction. The high-Mr fraction has been shown to consist of the low-Mr nitrite reductase enzyme associated with a hydrophobic 'binding protein'. The amino acid composition for both proteins is reported. The nitrite reductase enzyme shows spectral characteristics indicative of the presence of c-type haem groups. Measurements at 610 nm indicate the presence of some high-spin haem groups at neutral pH. This haem subgroup undergoes a pH-linked high-spin - low-spin transition at alkaline pH. Approximately two of the six haem groups present within the enzyme bind CO with low affinity (KD = 0.4 mM). The enzyme also shows a range of redox activities with various inorganic reagents. The enzyme has been shown to exhibit dithionite reductase, oxygen reductase and CO2 reductase activities.

Amino Acids↗
PubMed1986

Kinetic studies on the nitrite reductase of Wolinella succinogenes.

The six haem groups of the nitrite reductase enzyme isolated from Wolinella succinogenes are rapidly reduced by the addition of dithionite (S2O4(2-)). The reduction, however, is not homogeneous. Two of the haem groups, namely those that show spectral characteristics typical of five-co-ordinated haem groups, are reduced in a dithionite-concentration-dependent fashion with a rate limit of 1.5 S-1. The other four haem groups, which show spectral characteristics very similar to those of normal six-co-ordinate c-haem groups, reduce in a linear dithionite-concentration-dependent manner with a second-order rate constant of 150 M-1/2 X S-1. The ratio of the amplitudes of the two reduction phases observed in stopped-flow studies is found to be dependent on the concentration of dithionite used. A model is proposed to account for these observations, and computer simulations show that the model represents a good fit to the experimental data. The two haem groups with five-co-ordinate spectral characteristics bind CO. Flash photolysis of the CO complex exhibits one major recombination process with a linear dependence in rate on CO concentration with a second-order rate constant of 2 X 10(6) M-1 X S-1. By contrast, stopped-flow mixing of the reduced protein with CO shows a very complex pattern of combination, with most of the observed absorbance change associated with a concentration-independent step. These findings are rationalized in terms of structural changes in the protein consequent to ligand binding.

Bacteroidaceae↗
PubMedDate not supplied

A long-term follow-up of dietary advice in maturity onset diabetes: the experience of one centre in the UK prospective study.

The efficacy of simple dietary advice in 65 patients followed for 3 years at one centre participating in the UK prospective study of maturity onset diabetes was assessed. Whereas normal weight patients tended to keep to the prescribed calories, overweight patients tended to eat more. Total carbohydrate content was unchanged but there was a significant increase in unrefined carbohydrate and fibre.

Adult↗