An in vitro approach for demonstrating the critical role of serum albumin in the detoxication of the carbamate carbaryl at in vivo toxicologically relevant concentrations.

The hydrolysis of carbaryl by bovine serum albumin (BSA) was studied at toxicologically relevant concentrations (range 15-300 microM) in order to determine the role of this protein in the detoxication of the carbamate in vivo. The 1-naphthol released during the hydrolysis of carbaryl was monitored using gas chromatography coupled with mass spectrometry. BSA hydrolyzed carbaryl in a time-progressive way. The hydrolysis was also dependent of enzyme (1.0, 2.5, 5.0 and 7.0 mg ml(-1)) and substrate (range between 15 and 1,000 microM) concentration. The estimated turnover number and Michaelis-Menten constant were 1.6 x 10(-4) s(-1) and 430 microM, respectively. Thus, the second order rate constant was 0.37 M(-1) s(-1). At enzyme concentrations of 7.0 mg ml(-1) and substrate concentrations ranging between 50 and 300 microM about 80% of substrate was hydrolyzed in 3 h. At lower substrate concentrations (15 and 30 microM carbaryl) also significant hydrolysis was detected at the highest enzyme concentration, even when these substrate concentrations were 30 and 15 times lower than the Michaelis-Menten constant. Although the efficacy of the enzymatic hydrolysis is low, the extrapolation of our results to the physiological albumin high concentrations (around 40 mg ml(-1)) suggests that the hydrolysis of carbaryl by serum albumins plays a critical role in the detoxication of this carbamate at in vivo toxicologically relevant concentrations.