Polyphenolic Antioxidants Efficiently Protect Urease from Inactivation by Ultrasonic Cavitation

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Inactivation of urease (25 nM) in aqueous solutions (pH 5.0–6.0) treated with low-frequency ultrasound (LFUS; 27 kHz, 60 W/cm2, 36–56°C) or high-frequency ultrasound (HFUS; 2.64 MHz, 1 W/cm2, 36 or 56°C) has been characterized quantitatively, using first-order rate constants: kin, total inactivation; k*in, thermal inactivation; and kin(us), ultrasonic inactivation. Within the range from 1 nM to 10 μM, propyl gallate (PG) decreases by approximately threefold the rate of LFUS-induced inactivation of urease (56°C), whereas resorcinol poly-2-disulfide stops this process at 1 nM or higher concentrations. PG completely inhibits HFUS-induced inactivation of urease at 1 nM (36°C) or 10 nM (56°C). At 0.2–1.0 μM, human serum albumin (HSA) increases the resistance of urease treated with HFUS to temperature- and cavitation-induced inactivation. Complexes of gallic acid polydisulfide (GAPDS) with HSA (GAPDS–HSA), formed by conjugation of 1.0 nM GAPDS with 0.33 nM HSA, prevent HFUS-induced urease inactivation (56°C).

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