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Differentiating the effects of microwave and heat on tissue proteins and their crosslinking by formaldehyde
1Department of Pathology, Ninewells Hospital and Medical School, Dundee, UK.
Abstract:
Alkaline phosphatase activity in mouse liver blocks, cooled by an ice-bath, decreased by 50% in 5 min of microwave irradiation (280 W). This loss of protein tertiary structure has been mirrored by ultrastructural changes in the same tissue. Microwave irradiation did not produce cleavage or polymerization of lysozyme or haemoglobin. Protein formaldehyde reaction mixtures produced protein polymers between 0 degree and 40 degrees C which could be separated by SDS-polyacrylamide gel electrophoresis. Microwave irradiation of lysozyme or haemoglobin plus formaldehyde on ice-bath up to 30 min produced a similar electrophoretic pattern. When lysozyme or haemoglobin plus formaldehyde was heated to 60 degrees C for 30 min, the protein polymers migrated faster on electrophoresis, suggesting a smaller hydrodynamic volume than expected due to intramolecular crosslink formation, not opened up under the conditions of electrophoresis.
Insights
Microwave irradiation significantly reduces alkaline phosphatase activity and alters protein structure in mouse liver. However, it does not cause protein cleavage or polymerization, even when combined with formaldehyde.
Area of Science:
- Biochemistry
- Protein Chemistry
- Biophysics
Background:
- Microwave irradiation is increasingly used in biological research and diagnostics.
- Understanding its effects on protein structure and function is crucial for accurate interpretation of results.
- Previous studies have shown varied effects of microwaves on biological molecules.
Purpose of the Study:
- To investigate the impact of microwave irradiation on protein structure and activity.
- To determine if microwave irradiation induces protein cleavage or polymerization.
- To explore the interaction of microwave irradiation with formaldehyde in protein modification.
Main Methods:
- Assessing alkaline phosphatase activity in mouse liver tissue after microwave irradiation.
- Examining ultrastructural changes in microwave-irradiated liver tissue using electron microscopy.
- Studying the effects of microwave irradiation on lysozyme and hemoglobin, both alone and in combination with formaldehyde.
- Analyzing protein polymers formed in formaldehyde reaction mixtures using SDS-polyacrylamide gel electrophoresis.
Main Results:
- Microwave irradiation (280 W) for 5 minutes at 0°C caused a 50% decrease in alkaline phosphatase activity in mouse liver, accompanied by ultrastructural changes.
- Microwave irradiation alone did not lead to cleavage or polymerization of lysozyme or hemoglobin.
- Protein polymers were formed in mixtures of protein and formaldehyde between 0°C and 40°C, separable by SDS-PAGE.
- Microwave irradiation of lysozyme or hemoglobin with formaldehyde on ice produced similar electrophoretic patterns to thermal polymerization.
- Heating protein-formaldehyde mixtures to 60°C resulted in faster migration on electrophoresis, indicating intramolecular crosslinking.
Conclusions:
- Microwave irradiation can significantly alter protein tertiary structure and enzyme activity.
- Microwave irradiation does not directly cause protein cleavage or polymerization.
- Formaldehyde can induce protein polymerization, and microwave irradiation under specific conditions can influence this process.
- Intramolecular crosslinking may occur in proteins heated with formaldehyde, affecting their hydrodynamic volume.