Non-thermal effects of electromagnetic fields at mobile phone frequency on the refolding of an intracellular protein: myoglobin.

Abstract

Non-thermal effects induced by exposure to microwave electromagnetic field (MW-EMF) at 1.95 MHz, a frequency used in mobile communication, have been observed on the refolding kinetics of the heme binding site in an intracellular protein: tuna myoglobin, starting from acidic conditions. We have selected myoglobin because it can be considered a good model to study protein interactions with MW-EMF for its well-known high-resolution crystallographic structure. Myoglobin solutions at pH 3.0 were subjected to 3 h exposure to microwave field (with a specific absorption rate of 51 +/- 1 mW/g); the heme site refolding has been followed by measuring the molecular absorption in the Soret spectral region and the data were fitted to a bi-exponential model. The kinetics of exposed samples appear to be slowered by MW-EMF action. Moreover, the tryptophanyl lifetime distribution of the exposed protein, as deduced by the analysis of the fluorescence emission decay from its single tryptophan, appears sharper if compared to non-exposed protein samples. This observation suggests that the presence of MW-EMF could affect the propensity of protein molecules to populate specific conformational substates among which myoglobin molecules fluctuate at acidic pH. Changes in the structural fluctuation caused by MW perturbation can affect differently the aggregation process that occurs competitively during the protein folding, so representing a potential risk for protein "misfolding." These data suggest that MW-EMF could have also biochemical and, consequently, biological effects on eukaryotic cells that are still under investigation.

AI evidence extraction

Main findings

Myoglobin solutions (pH 3.0) exposed for 3 h to a microwave electromagnetic field (SAR 51 +/- 1 mW/g) showed slower refolding kinetics of the heme binding site compared with non-exposed samples. The tryptophanyl lifetime distribution of exposed protein appeared sharper than in non-exposed samples.

Outcomes measured

• Refolding kinetics of the heme binding site in tuna myoglobin (bi-exponential fit to Soret absorption)
• Tryptophanyl fluorescence lifetime distribution (single tryptophan)
• Protein conformational substates/structural fluctuation at acidic pH (inferred from fluorescence lifetime distribution)

Limitations

• In vitro protein solution model (tuna myoglobin) under acidic conditions (pH 3.0), limiting generalizability to cells/organisms
• Sample size not reported in abstract
• Only one exposure condition and duration reported in abstract
• Mechanistic/biological implications (e.g., misfolding risk, effects in eukaryotic cells) are suggested but not directly demonstrated

Suggested hubs

• mobile-phones-rf (0.86)
  Exposure described as a mobile communication frequency microwave field with SAR reported.

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    "study_type": "in_vitro",
    "exposure": {
        "band": "microwave",
        "source": "mobile phone",
        "frequency_mhz": 1.9499999999999999555910790149937383830547332763671875,
        "sar_wkg": 51,
        "duration": "3 h"
    },
    "population": null,
    "sample_size": null,
    "outcomes": [
        "Refolding kinetics of the heme binding site in tuna myoglobin (bi-exponential fit to Soret absorption)",
        "Tryptophanyl fluorescence lifetime distribution (single tryptophan)",
        "Protein conformational substates/structural fluctuation at acidic pH (inferred from fluorescence lifetime distribution)"
    ],
    "main_findings": "Myoglobin solutions (pH 3.0) exposed for 3 h to a microwave electromagnetic field (SAR 51 +/- 1 mW/g) showed slower refolding kinetics of the heme binding site compared with non-exposed samples. The tryptophanyl lifetime distribution of exposed protein appeared sharper than in non-exposed samples.",
    "effect_direction": "harm",
    "limitations": [
        "In vitro protein solution model (tuna myoglobin) under acidic conditions (pH 3.0), limiting generalizability to cells/organisms",
        "Sample size not reported in abstract",
        "Only one exposure condition and duration reported in abstract",
        "Mechanistic/biological implications (e.g., misfolding risk, effects in eukaryotic cells) are suggested but not directly demonstrated"
    ],
    "evidence_strength": "low",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "microwave electromagnetic field",
        "MW-EMF",
        "non-thermal effects",
        "mobile communication frequency",
        "myoglobin",
        "protein refolding",
        "heme binding site",
        "Soret absorption",
        "fluorescence lifetime",
        "tryptophan",
        "conformational substates",
        "protein misfolding"
    ],
    "suggested_hubs": [
        {
            "slug": "mobile-phones-rf",
            "weight": 0.85999999999999998667732370449812151491641998291015625,
            "reason": "Exposure described as a mobile communication frequency microwave field with SAR reported."
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    ]
}

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