Chloroperoxidase-mediated oxidation of 1,3-butadiene to 3-butenal, a crotonaldehyde precursor.

Previously, we have shown that 1,3-butadiene, a rodent and possibly a human carcinogen, can be oxidized by chloroperoxidase-H2O2 at pH 7.4 to yield the potent mutagens, butadiene monoxide and crotonaldehyde. Because the crotonaldehyde/butadiene monoxide ratio from reactions with chloroperoxidase was higher than that obtained from reactions with myeloperoxidase or cytochrome P450 enzymes, in the present study, the chloroperoxidase reaction was further investigated in an attempt to define optimal conditions for catalysis and to possibly obtain direct evidence for the formation of the crotonaldehyde precursor 3-butenal in these incubations. The results showed that butadiene monoxide and crotonaldehyde formation was optimal at pH 6.0. As opposed to incubations carried out at pH 7.4, GC analyses of incubations carried out at pH 4.5, 5.0, and 6.0 demonstrated the presence of a new peak which had a retention time different from that of butadiene monoxide and crotonaldehyde. The new peak was identified as 3-butenal by comparison of its retention time and mass spectrum with those of reference material. Evidence for 3-butenal being a precursor of crotonaldehyde was obtained by the findings that 3-butenal was not simply a decomposition product of butadiene monoxide or crotonaldehyde under the incubation or assay conditions, and that the 3-butenal/crotonaldehyde ratio decreased when the incubation time was increased between 5 and 30 min or when the incubation temperature was increased between 10 and 45 degrees C. The combined 3-butenal and crotonaldehyde concentrations remained constant at the various incubation temperatures. Furthermore, 3-butenal conversion to crotonaldehyde was faster at pH 7.4, compared to pH 6.0.(ABSTRACT TRUNCATED AT 250 WORDS)