The two substrates (x-3 andx-6) with a pentadienyl system positioned at thex-6
position were oxygenated by SBLOX-1 at the highest rate, while the other three
substrates were oxygenated at 20 % (x-7), 25 % (x-5) and 60 % (x-4) of that of
AA (x-6).
The influence of the chain length of substrates bearing a 1Z,4Zpentadienyl system
located at thex-6 position was also studied in detail (Matsui et al., 1992) using an
entire series of (x 6 Z,x 9 Z)-C 13 C 24 dienoic acids and SBLOX-1 (Figure 6). It was
shown that the rates of oxygenation of the C 18 ,C 19 ,C 20 (maximum) and C 21 dienoic
acids were the highest. For C 17 and C 22 dienoic acids, the rates of oxygenation were
60 % of that of LA (C 18 ), while those of C 16 ,C 23 and C 24 dienoic acids fell between
20 % and 30 %. For lower chain lengths (C 15 ,C 14 and C 13 ) acids, the rates of oxy-
genation were insignificant.
Beside needing a correct positioning of the pentadienyl system around the n-6
position, SBLOX-1 substrates must also possess an anionic ionizable group at
one end of the carbon chain. While this requirement is fulfilled in natural substrates
by the presence of the carboxylate group, it has been shown that a sulfate group could
also be used (Bild et al., 1977a). By contrast, methyl esters (Hatanaka et al., 1984) or
triglycerides of PUFA are poor substrates for SBLOX-1, leading to low yields in
HPODs and a far less product specificity. Dienols synthesized by the reduction
of the carboxylate group of natural PUFAs are also oxygenated at a rate lower of
that of the parent compounds (20 % for example for the dienol arising from LA)
and with a far less product specificity (Hatanaka et al., 1989). On the other
hand, Brash and co-workers have shown that linoleic and arachidonic acids ester-
ified in phosphatidylcholine could be oxygenated by SBLOX-1 (20–30 % of the
rate of free acids) with no loss in product specificity (Brash et al., 1987). Finally, it
should be noted that anacardic acid (Figure 7), a constituent of cashew nut shells
(Anacardium occidentaleL.) is a substrate of SBLOX-1, with dioxygen being in-
serted at thex-4 position (Shoba et al., 1992).
16.3 Substrate and product specificities of lipoxygenases 345
Figure 6. Oxygenation of a series of (x 6 Z,x 9 Z)-C 13 C 24 dienoic acids catalyzed by SBLOX-1
(Matsui et al., 1992).
Figure 7. Anacardic acid, a substrate of SBLOX-1 (Shoba et al., 1992).