Inactivation of Glucose-6-Phosphate Dehydrogenase in Solution by Low- and High-Frequency Ultrasound |
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Authors: | Rachinskaya Zh V Karasyova E I Metelitza D I |
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Institution: | (1) Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, ul. Kuprevicha 5/2, Minsk, 220141, Belarus |
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Abstract: | We compared the kinetics of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) inactivation in 0.1 M phosphate buffer (pH 7.4) at 36–50° under conditions of exposure to low-frequency (LF, 27 kHz, 60 W/cm2) or high-frequency (HF, 880 kHz, 1.0 W/cm2) ultrasound (USD). The inactivation of G6PDH was characterized by effective first-order rate constants: k
in, total inactivation; k
in
*, thermal inactivation; and k
in(usd), ultrasonic inactivation. Dilution of the enzyme solution from 20 to 3 nM was accompanied by a significant increase in the values of the three rate constants. The following inequality was valid in all cases: k
in > k
in
*. The rate constants increased with temperature. The Arrhenius plots of the temperature dependences of k
in and k
in(usd) had an break point at 44°C. The activation energy (
act) of the total inactivation of G6PDH was higher than
act for the process of ultrasonic inactivation of this enzyme. The two values were found to depend on USD frequency:
act was higher in the case of inactivation with low-frequency ultrasound (LF-USD) than high-frequency ultrasound (HF-USD). The rate of the ultrasonic inactivation of this enzyme substantially decreased in the presence of low concentrations of HO. radical scavengers (dimethylformamide, ethanol, and mannitol). This fact supports the conclusion that free radicals are involved in the mechanism of G6PDH inactivation in solutions exposed to LF-USD and HF-USD. Ethanol was an effective protector of G6PDH inactivation in solutions exposed to USD. |
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Keywords: | |
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