Year

2005

Degree Name

Doctor of Philosophy

Department

Department of Chemistry - Faculty of Science

Abstract

This thesis describes a spectroscopic investigation of the effects of pulsed electromagnetic radiation on the conformation, unfolding, aggregation and precipitation of a variety of proteins. Initial experiments required the calibration of a microwave exposure system thus the temperature of different buffer solutions was studied in detail. The exposure system comprised of an incubator and a rebuilt domestic microwave oven that delivered pulses every six minutes to give a plot of the temperature before, during and after a pulse period of microwaves. All solutions returned to their baseline temperature prior to the next pulse period. The effect of exposure to microwave pulses of several seconds duration on the aggregation rate of six stressed target proteins (alcohol dehydrogenase, bovine serum albumin, catalase, citrate synthase, insulin and ovotransferrin) was examined in solution. The hypothesis tested was that the initial rate of precipitation of samples exposed to microwave pulses once every six minutes was significantly higher than that of a control held at the same average temperature. The results show statistical significance to confirm the hypothesis in all cases except for insulin, bovine serum albumin and citrate synthase when the latter two proteins were maintained at an average temperature of 45oC and 37oC respectively. In these exceptional cases, the microwave induced temperature excursion was not expected to induce a change in the precipitation rate on the basis of previous knowledge of the unfolding behaviour of the proteins. The second hypothesis tested was that the molecular chaperone, α-crystallin prevents the aggregation and precipitation of target proteins under the above regimes. It was found that α-crystallin suppressed precipitation but it was not as effective when proteins were also exposed to pulsed microwaves. The effect of exposure to 50 Hz DC and AC electric field was examined on stressed alcohol dehydrogenase and citrate synthase. The hypothesis tested was that the initial rate of precipitation of samples exposed to microwave pulses once every six minutes was significantly higher than that of a control held at the same average temperature. This was not detected. When a difference could be detected, it was only observed in a increase or decrease in precipitation, well after exposure.The results of this thesis are relevant to the setting of standards for microwave exposure as they show that a six-minute averaging period of temperature is not appropriate in the prediction of protein unfolding.

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