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G W Niven

Publications and source records attributed to G W Niven.

7 recordsLinked to original sources
PubMed1998

Aqueous two-phase systems: a novel approach for the separation of proteose peptones.

Poly(ethylene glycol) and dextran aqueous two-phase systemis (ATPS) were developed to facilitate the separation of components of the proteose peptone fraction of bovine milk, which are mostly large casein derived peptides or glycoproteins. These have proved difficult to purify using conventional chromatographic procedures. ATPS exploit differences in hydrophobicity, size and ionic properties of the proteose peptones with a view to developing methods for future large scale preparations of the individual components of this whey protein fraction.

Amino Acid Sequence↗
PubMed1998

Changes in the concentrations of free amino acids in milk during growth of Lactococcus lactis indicate biphasic nitrogen metabolism.

Analysis of the concentrations of free amino acids in milk during growth of Lactococcus lactis subsp, lactis revealed a biphasic pattern of change during the logarithmic phase. During the first period there was little overall change in the total concentration of amino acids in the medium. The second phase was characterized by increased net liberation of free amino acids. There were also qualitative differences in the amino acids that were taken up and utilized during each period. The concentrations of Val, Leu and Ile decreased only during the early phase, while those of Ser, Arg, Thr and Met decreased only during the second phase. Gly and Ala were utilized throughout logarithmic growth. Gly uptake appeared to be greater during the second period and accounted for the largest proportion of free amino acid utilization at this time. It is possible that the biphasic nature of amino acid nutrition was due to increased consumption in late log phase of peptides derived from milk proteins by proteolysis. Increased activity of the arginine deiminase pathway during late log phase was inferred from increased utilization of Arg and liberation of citrulline and ornithine.

Amino Acids↗
PubMed1998

Cell membrane integrity and lysis in Lactococcus lactis: the detection of a population of permeable cells in post-logarithmic phase cultures.

A method was developed that enabled an analysis of the proportion of permeable cells in a culture of Lactococcus lactis. This used the fluorescence of propidium iodide (PI) when in contact with DNA and the impermeability of the intact cell membrane to this compound. A permeability index was suggested that expresses the PI-induced fluorescence of a cell suspension as a percentage of the value obtained from wholly permeabilized cells after treatment with cetyltrimethylammonium bromide. This method was applied to the determination of cell permeability in death phase cultures. A large proportion of unlysed cells was freely permeable to PI, a finding that may have some significance for the investigation of the role of cell lysis in cheese maturation. This method is suggested as a useful addition to the techniques available for the study of cell damage in a variety of fields, and for the screening of cheese starter bacteria.

Bacteriolysis↗
PubMed1995

The characterization of two aminopeptidase activities from the cyanobacterium Anabaena flos-aquae.

Aminopeptidase activity, indicated by hydrolysis of the synthetic substrate alanine p-nitroanilide, was identified in the cyanobacterium Anabaena flos-aquae. On purification, 2 enzymes were separated by gel filtration chromatography, a 188 kDa multimer (AP-I) and a 59 kDa monomeric metalloprotein (AP-II). Their activities against a range of alanine-containing peptides were screened. Both enzymes were capable of removing a variety of N-terminal residues, including proline. Neither removed N-terminal acidic residues. The activity of AP-I appeared to be limited to di- and tri-peptides, while AP-II was capable of hydrolysing (Ala)5. It was not possible to assign the active-site chemistry of AP-I to one of the known hydrolase subgroups as none of the potential inhibitors tested had a significant inhibitory effect. This is the first reported purification of aminopeptidases from a cyanobacterium.

Aminopeptidases↗
PubMed1995

A study of the substrate specificity of aminopeptidase N from Lactococcus lactis subsp. cremoris Wg2.

A systematic study was made of the ability of aminopeptidase N from Lactococcus lactis subsp. cremoris Wg2 to hydrolyse different peptide substrates. The enzyme showed a marked preference for substrates containing arginine as the N-terminal residue but, to a lesser extent, was also capable of cleaving other residues such as lysine and leucine. There was a tendency for the activity to increase with the hydrophobicity index of the C-terminal residue of dipeptide substrates. It was also observed that the enzyme tended to have higher affinities but lower Vmax values for tripeptides with hydrophobic C-terminal residues. The values determined for Km and Vmax increased with chain length for oligopeptides of the general formula Lys-Phe-(Gly)n, the optimum, as determined from Vmax/Km, being when n = 4. Typical Km values for the most effective substrates were in the range 0.2-0.6 mM.

Amino Acid Sequence↗
PubMed1993

A method for the continuous purification of proteins by affinity adsorption.

A method was conceived for the purification of biomolecules on a continuous-flow basis using affinity adsorption. The affinity ligand was bound to a nylon belt which was passed sequentially through four chambers to which flows of feedstock, wash medium, eluent and regeneration medium were applied. The target compound was thus removed from the feedstock stream and desorbed into a continuous flow of eluent. Prototype laboratory-scale apparatus was designed and constructed and the technical feasibility of this method was demonstrated using soybean trypsin inhibitor as a ligand for the adsorption of trypsin. The effects of various operational parameters on apparatus function were investigated using this model system. In addition, continuous removal of trypsin from a bovine pancreatic extract was carried out during an 8 h experiment.

Adsorption↗