p-Nitrosodimethylaniline (RNO) bleaching by soybean lipoxygenase-1. Biochemical characterization and coupling with oxodiene formation

In this paper, a novel reaction catalysed by the soybean lipoxygenase-1 (li noleate:oxygen oxidoreductase, EC 1.13.11.12) (LOX-1) is reported: p-nitros odimethylaniline (RNO) bleaching. RNO bleaching in the course of the LOX-1 reaction (with linoleate as substrate) was followed by monitoring photometr ically at 440 nm the absorbance decrease of the test sample. The appearance of oxodienes, a class of compounds produced during the same reaction, was also studied. This was carried out by monitoring the absorbance increase at 285 nm in the course of the LOX-1 reaction. RNO bleaching and oxodiene for mation by soybean LOX-1 were found to occur synchronously. They occurred on ly under conditions of limited oxygen; moreover, both reactions showed satu ration kinetics as expected for enzyme-catalysed reactions, had similar dep endence on pH and temperature (pH optima about 9, temperature optima about 45 degreesC) and were competitively inhibited by n-propylgallate (PG), a fr ee radical scavenger. Finally, the occurrence of both reactions was found t o depend on the presence of 13-hydroperoxy-linoleate, the primary product o f the aerobic LOX reaction and was found to be not related with the beta -c arotene bleaching catalysed by the same enzyme. The possible molecular basi s of the link between RNO bleaching and oxodiene formation in the course of the anaerobic soybean LOX-1 reaction is discussed. (C) 2000 Editions scien tifiques et medicales Elsevier SAS.