Biomedical subjects

E K Murray

Publications and source records attributed to E K Murray.

3 recordsLinked to original sources

PubMed1985

Conformational changes in the (Ca2+ + Mg2+)-ATPase of sarcoplasmic reticulum detected using phosphorescence polarization.

The technique of time-averaged phosphorescence has been used to study the interaction of calcium ions and ATP with the (Ca2+ + Mg2+)-ATPase in sarcoplasmic reticulum vesicles. The presence of excess calcium ions was found to cause a 20% decrease in the phosphorescence emission anisotropy. This is interpreted as being due to a conformational change in the protein and is supported by data from time-resolved phosphorescence measurements which also show a lowering of the anisotropy. This change in the decay of the emission anisotropy is associated with only minor changes in the rotational relaxation time of the protein and is again suggestive of a conformational change in the protein. In some cases ATP was also observed to lower the time-averaged phosphorescence anisotropy possibly via an interaction with the low-affinity regulatory site of the protein.

Adenosine Triphosphate↗

PubMed1984

Rotational diffusion of calcium-dependent adenosine-5'-triphosphatase in sarcoplasmic reticulum: a detailed study.

The Ca2+-Mg2+ adenosine-5'-triphosphatase (ATPase) in sarcoplasmic reticulum has been covalently labeled with the phosphorescent triplet probe erythrosinyl 5-isothiocyanate. The rotational diffusion of the protein in the membrane at 25 degrees C was examined by measuring the time dependence of the phosphorescence emission anisotropy. Detailed analysis of both the total emission S(t) = Iv(t) + 2IH(t) and anisotropy R(t) = [Iv(t) - IH(t)]/[Iv(t) + 2IH(t)] curves shows the presence of multiple components. The latter is incompatible with a simple model of protein movement. The experimental data are consistent with a model in which the sum of four exponential components defines the phosphorescence decay. The anisotropy decay corresponds to a model in which the phosphor itself or a small phosphor-bearing segment reorients on a sub-microsecond time scale about an axis attached to a larger segment, which in turn reorients on a time scale of a few microseconds about an axis fixed in the frame of the ATPase. A fraction of the protein molecules rotate on a time scale of 100-200 microseconds about the normal to the bilayer, while the rest are rotationally stationary, at least on a sub-millisecond time scale.

Animals↗

PubMed1983

Monitoring membrane protein rotational diffusion using time-averaged phosphorescence.

Rotational motions of membrane proteins have previously been measured using time-dependent phosphorescence techniques. This paper discusses a method of examining membrane protein mobility at temperatures relevant to biological systems, using a technique similar to steady-state fluorescence. The method is demonstrated using sarcoplasmic reticulum ATPase labelled with erythrosin isothiocyanate, both in its natural condition and crosslinked by incubation with glutaraldehyde. The experimentally-observed dependence of phosphorescence anisotropy on temperature is compared to a calculated anisotropy-temperature curve. Comparison is made between the anisotropy decay curves obtained by time-averaged phosphorescence and steady-state fluorescence.

Animals↗