16.1 Introduction
Lipoxygenases (LOXs) are nonheme iron dioxygenases (Galliard and Chan, 1980;
Vliegenthart and Veldink, 1982; Vick and Zimmerman, 1987; Siedow, 1991; Gard-
ner, 1991; 1996; Yamamoto, 1991; Ford-Hutchinson et al., 1994; Lehman, 1994;
Ku ̈hn and Thiele, 1995; Piazza, 1996) which catalyze the stereospecific incorpora-
tion of dioxygen into the 1,Z-4,Zpentadienyl system of polyunsaturated fatty acids
(PUFAs) to generate optically active conjugated dienic hydroperoxides (Figure 1).
LOXs are ubiquitous eukaryotic enzymes found in yeasts (Shechter and Gross-
man, 1983), filamentous fungi (Matsuda et al., 1978), macroscopic fungi (Grosch
and Wurzenberger, 1984), algae (Hamberg and Gerwick, 1993), bryophytes (Mat-
sui et al., 1991), vascular plants (Siedow, 1991), corals (Bundy et al., 1986), fishes
(Hsieh et al., 1988) and mammals (Yamamoto, 1991). Generally speaking, LOXs
display a very high regiospecificity (position of oxygenation) and a very high stereo-
specificity (configuration of the two conjugated double bonds and absolute config-
uration of the formed asymmetric carbon bearing the hydroperoxide function). LOXs
are classified with respect to their regiospecificity using either linoleic acid (LA)
with vegetal LOXs or arachidonic acid (AA) with other LOXs. For example soy-
bean LOX isoenzyme-1 (SBLOX-1) is classified as a 13-LOX, whereas potato tuber
LOX is classified as a 9-LOX when LA is used as substrate (Figure 2).
It should be noted that despite an opposite regiospecificity, the two enzymes yield
both a hydroperoxide (HPOD) ofSabsolute configuration, bearing a 2E,4Zconju-
gated dienic system.
With AA as substrate, various positions could be oxygenated depending on the
regiospecificity of the enzyme used. The most encountered LOXs are 5-, 8-, 12-
and 15-LOXs. It should be stressed that a 13-LOX (LA) will be classified as a
15-LOX (AA), one speaks of a (n-6)-LOX, and that a 9-LOX (LA) will oxygenate
AA mainly at the 5 position (5-LOX).
338 16 Properties and Applications of Lipoxygenases
Figure 1. Reaction catalyzed by LOXs.
Figure 2. Opposite regiospecificities shown by two plant LOXs with LA as substrate.