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Abnormalities in the microsomal oxidases of the WHO standard reference strain of Musca domestica
Abstract:
Observations made during biochemical and toxicological studies of the housefly, in which the WHO standard reference (SR) strain was used as a standard, indicated that this strain differs from other strains in certain physiological and toxicological aspects. Experiments are described in which microsomal oxidases prepared from the standard reference strain and several other housefly strains, both susceptible and resistant to insecticides, were compared for heat stability, sensitivity to ionic strength, pH optima, and the spectral characteristics of their cytochrome P-450. In a comparison with 8 strains the SR strain microsomes were more stable at high incubation temperatures (40-47.5 degrees C). Compared to two other strains (NAIDM, susceptible, and Isolan-B, resistant) SR was more stable at low pH and more sensitive to high ionic strength. In spectral comparisons with NAIDM and Isolan-B, SR was found to contain microsomal cytochrome P-450 that differed slightly in its carbon monoxide or octylamine binding spectra. The results suggest that this strain may not provide a suitable reference in studies involving the microsomal oxidases. However, these apparent differences should not reduce the value of the SR stain as a reference in insecticide resistance studies.
Insights
The WHO housefly reference strain exhibits unique physiological and toxicological properties, particularly in its microsomal oxidases. These differences suggest it may not be ideal for general microsomal oxidase research but remains valuable for insecticide resistance studies.
Area of Science:
- Biochemistry
- Toxicology
- Entomology
Background:
- The World Health Organization (WHO) standard reference (SR) housefly strain is widely used in toxicological and biochemical studies.
- Previous observations suggest potential physiological and toxicological differences in the SR strain compared to others.
Purpose of the Study:
- To investigate and compare the biochemical and toxicological characteristics of microsomal oxidases from the WHO SR housefly strain against other susceptible and resistant strains.
- To evaluate the suitability of the SR strain as a reference in studies involving housefly microsomal oxidases.
Main Methods:
- Preparation and comparison of microsomal oxidases from the SR strain and eight other housefly strains.
- Analysis of enzyme properties including heat stability, ionic strength sensitivity, pH optima, and cytochrome P-450 spectral characteristics.
Main Results:
- SR strain microsomes demonstrated greater stability at high incubation temperatures (40-47.5°C) and low pH.
- SR strain microsomes were more sensitive to high ionic strength compared to other strains.
- Spectral analysis revealed slight differences in cytochrome P-450 carbon monoxide and octylamine binding spectra for the SR strain.
Conclusions:
- The unique biochemical properties of the SR housefly strain's microsomal oxidases suggest it may not be a universally suitable reference for all microsomal oxidase studies.
- Despite these biochemical distinctions, the SR strain retains its value as a reference standard specifically for insecticide resistance research.
