Coupled oxidation of carotene and linoleate catalyzed by lipoxidase.

The coupled oxidation of carotenoids and certain unsaturated fatty acids by lipoxidase has long been of interest. It not only has economic importance because of destruction of a valuable feed constituent, carotene, but is an apparently unique enzymatic reaction, regarded by some as an example of a free radical chain reaction in a polyphase system (1). Although considerable work has been done on the coupled oxidation of carotene and linoleic acid by lipoxidase, most workers have devoted themselves to measuring one or a combination of two of the variables: carotene, linoleic acid, and oxygen (l-5). The presently described system was developed in order to measure simultaneously all three of these variables. The substrate here presented is an apparently homogeneous aqueous dispersion of carotene and sodium linoleate. Unlike a previously reported substrate for lipoxidase (6), this substrate shows the spectral absorption peaks characteristic of carotene dissolved in organic solvents. An anomalous maximum in carotene destruction at low levels of linoleic acid has been reported (2, 6). A similar phenomenon is shown here for diene conjugation. Both maxima correspond to the critical micelle concentration of sodium linoleate.