Biomedical subjects

J Bramhall

Publications and source records attributed to J Bramhall.

21 records · Page 2Linked to original sources

PubMed1978

Photoreactive probes for high resolution mapping of membrane proteins.

The preparation and characterization of a novel series of radioactively labeled membrane probes is described. These probes are carbohydrate derivatives of fatty acids which contain a photosensitive azide moiety at a specified distance along the alkyl chain. The function of the carbohydrate group is to restrict the azide function to the outer surface monolayer of sealed membrane systems. The azide probes have been used in several well-characterized membrane systems including erythrocyte ghosts, membrane-enveloped viruses, and artificial vesicles. Upon activation, the probes attach to integral proteins to form a stable, covalent complex which may be extracted and identified. The activation protocol is outlined and some of the preliminary results are discussed.

Azides↗

PubMed1976

A new rapid assay of oestrogens in pregnancy urine using the substrate native fluorescence.

A simple and rapid method is described for the quantitative determinations of free and conjugated oestrogens in pregnancy urine. The oestrogens are precipitated with ammonium sulphate and freed from non-oestrogenic compounds by solvent extraction. The conjugated oestrogens are hydrolysed by a beta-glucuronidase from Escherichia coli, and the total free oestrogens are extracted into ether and their fluorescence intensity at 310 nm in this solvent is determined. The method is rapid and precise for oestrogen levels at concentrations greater than 2 mug/ml (7 mumol/1). It is proposed that this method, which measures oestradiol and oestriol levels, be applied routinely to monitor feto-placental function in pregnancy. It offers advantages over other currently used assays in that less manipulative and technical skill is required to give a high level of precision and accuracy. An accurate estimate can be produced within 30-60 min of receipt of a 24-h uring specimen. Two variations of the method are also described. In one the ammonium sulphate precipitation step is omitted so as to give an even quicker assay procedure which determines conjugated oestrogens in the urine, and in the other oestriol only is determined.

Estrogens↗

PubMedDate not supplied

Permeability of lipid bilayers to water and ionic solutes.

The lipid bilayer moiety of biological membranes is considered to be the primary barrier to free diffusion of water and solutes. This conclusion arises from observations of lipid bilayer model membrane systems, which are generally less permeable than biological membranes. However, the nature of the permeability barrier remains unclear, particularly with respect to ionic solutes. For instance, anion permeability is significantly greater than cation permeability, and permeability to proton-hydroxide is orders of magnitude greater than to other monovalent inorganic ions. In this review, we first consider bilayer permeability to water and discuss proposed permeation mechanisms which involve transient defects arising from thermal fluctuations. We next consider whether such defects can account for ion permeation, including proton-hydroxide flux. We conclude that at least two varieties of transient defects are required to explain permeation of water and ionic solutes.

Diffusion↗