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D McPhail

Publications and source records attributed to D McPhail.

5 recordsLinked to original sources
PubMed2000

Liposomes encapsulating polymeric chitosan based vesicles--a vesicle in vesicle system for drug delivery.

Drug delivery systems comprising vesicles prepared from one amphiphile encapsulating vesicles prepared from a second amphiphile have not been prepared previously due to a tendency of the bilayer components of the different vesicles to mix during preparation. Recently we have developed polymeric vesicles using the new polymer-palmitoyl glycol chitosan and cholesterol in a 2:1 weight ratio. These polymeric vesicles have now been encapsulated within egg phosphatidylcholine (egg PC), cholesterol (2:1 weight ratio) liposomes yielding a vesicle in vesicle system. The vesicle in vesicle system was visualised by freeze fracture electron microscopy. The mixing of the different bilayer components was studied by monitoring the excimer fluorescence of pyrene-labelled polymeric vesicles after their encapsulation within egg PC liposomes or hexadecyl diglycerol ether niosomes. A minimum degree of lipid mixing was observed with the polymeric vesicle-egg PC liposome system when compared to the polymeric vesicle-hexadecyl diglycerol ether niosome system. The polymeric vesicle-egg PC vesicle in vesicle system was shown to retard the release of encapsulated solutes. 28% of 5(6)-carboxyfluorescein (CF) encapsulated in the polymeric vesicle compartment of the vesicle in vesicle system was released after 4 h compared to the release of 62% of encapsulated CF from plain polymeric vesicles within the same time period.

Carbohydrate Sequence↗
PubMed1999

Crystallization and preliminary X-ray crystallographic analysis of a vancomycin-N-acetyl-D-Ala-D-Ala complex.

A vancomycin-N-acetyl-D-Ala-D-Ala complex has been crystallized by the sitting-drop vapour-diffusion method using imidazole maleic buffer at pH 7.6. The novel crystals obtained belong to the space group P6322 with unit-cell parameters a = b = 73.43 (1), c = 277.17 (4) A, gamma = 120 degrees. The crystal density was determined as 1. 106 g cm-3 which gives a supercell of 24 molecules (12 dimers) per asymmetric unit for an acceptable Matthews number and an estimated solvent content of 42%. Data were collected at room temperature to 2. 8 A.

Crystallization↗
PubMed1996

A reappraisal of the diversity and class distribution of aspartate transcarbamoylases in gram-negative bacteria.

Recently, the subunit composition of class A aspartate transcarbamoylases (ATCases) in fluorescent pseudomonads has been clarified. We present evidence that distribution of this type of ATCase may be more widespread than at first suspected. Bacterial ATCases exist in three forms: class A (molecular mass approximately 450-500 kDA); class B, typified by Escherichia coli ATCase (approximately 300 kDa); and class C, typified by Bacillus subtilis ATCase (approximately 100 kDa). Using gradient gel electrophoresis with activity-staining to scan bacterial sonicates, we report the existence of six more class ATCases. We have purified one of these, Acinetobacter calcoaceticus ATACase, and found its subunit composition to be similar to that of the pseudomonad ATCases. Two of these ATCases come from bacteria outside the gamma-subgroup of the Proteobacteria, one from the alpha-subgroup and one from Deinococcus radiophilus, a species phylogenetically remote from the Proteobacteria. Unexpectedly, three bacterial species, closely related to the fluorescent pseudomonads and acinetobacters, have ATCases of 100 kDa (class C). One of these, Stenotrophomonas (formerly Xanthomonas) maltophilia has been purified and found to be a homotrimer of 35 kDa polypeptide chains. We believe this is the first time that class C ATCases have been reported in Gram-negative bacteria. A distinctive cluster in the gamma-3 subgroup of the Proteobacteria is formed by the enteric bacteria and their relatives. So far only class B ATCases have been reported in this group. The evolutionary implications of these findings are discussed.

Acinetobacter calcoaceticus↗
PubMed1993

Purification of aspartate transcarbamoylase from Pseudomonas syringae.

The aspartate transcarbamoylase (ATCase) from Pseudomonas syringae has been purified. The purified enzyme was shown by SDS-PAGE to give two bands. Unambiguous results from N-terminal sequencing suggested that each band represented a homogeneous polypeptide. The M(r) (relative molecular mass) of the polypeptides was estimated to be 47 kDa and 34 kDa. The M(r) of the holoenzyme determined by gel filtration and electrophoretic migration in polyacrylamide gradient gels under non-denaturing conditions was estimated at approximately 490 kDa. These findings suggest a subunit structure different from any previously described for a bacterial ATCase.

Amino Acid Sequence↗