Medical/biological study (experimental study)

Non-Thermal effects in the microwave induced unfolding of proteins observed by chaperone binding med./bio.

By: George DF, Bilek MM, McKenzie DR

Published in: Bioelectromagnetics 2008; 29 (4): 342-330

Aim of study (acc. to author)

To study the effect of microwaves at 2450 MHz on protein (citrate synthase) unfolding.

Background/further details

The protein was exposed to microwaves only, conventional heat (water bath) only and combinations of heat and microwaves.
Unfolding proteins tend to bind to chaperones on their unfolding pathway and this attachment is monitored by surface plasmon resonance.

Endpoint

protein unfolding (citrate synthase)

Exposure

- 2.45 GHz
- microwaves
- microw. oven/heating device

Exposure	Parameters
Exposure 1: 2.45 GHz Modulation type: pulsed Exposure duration: continuous for 10, 15, and 20 s	SAR: 4.85 kW/kg mean

General information

The protein solution was subjected to microwave exposure, water bath for 5 min at 34 to 82.5 °C, and water bath at 29.5 to 44 °C followed by microwave exposure.

Exposure 1

Main characteristics

Frequency	2.45 GHz
Type	electromagnetic field
Exposure duration	continuous for 10, 15, and 20 s

Modulation

Modulation type	pulsed
Repetition frequency	50 Hz
Additional info	sharply peaked waveform having a peak to average ratio between 3:1 and 8:1 [Matsumoto et al., 2005]

Exposure setup

Exposure source	transformer type microwave oven with magnetron source
Chamber	A shelf made from high density polyethylene with holes fitting the Eppendorf tubes was located in the microwave oven cavity with a water ballast placed under it in a fixed spot in order to stabilise the field.
Setup	The protein solution in an Eppendorf tube of 80 µl volume was placed in the hole determined to have the maximum temperature rise.
Additional info	The temperature rise near the end-tip of the Eppendorf tube was measured over a volume of 0.8 mm side length using a fluoroptic probe.

Parameters

Measurand	Value	Type	Method	Mass	Remarks
SAR	4.85 kW/kg	mean	-	-	-

Measurement and calculation details

The waveform produced by the oven was examined using a dipole antenna coupled to an oscilloscope.

Reference articles

Matsumoto Y et al. (2005): Band-limitation effects on microwave oven noise in the 2.4-GHz band

Exposed system:

isolated bio./chem. substance

Methods Endpoint/measurement parameters/methodology

protein unfolding (citrate synthase, binding to a chaperone (alpha-crystallin; surface plasmon resonance)

Investigated system:

isolated bio./chem. substance

Time of investigation:

after exposure

Main outcome of study (acc. to author)

The data showed that microwaves caused a significantly higher degree of unfolding than conventional thermal stress for protein solutions heated to the same maximum temperature. The data support the hypothesis that microwaves have a non-thermal effect on protein conformation that could take the form of a direct interaction of the electromagnetic field with the protein or its water of hydration.

Study character:

medical/biological study
experimental study
full/main study

Study funded by

Australian Research Council (ARC)
Australian Research Council (ARC) Linkage Projects scheme

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