With this example it could be broadly concluded that the methodologies developed
for the use of SBLOX-1 could be applied to other LOXs, but that a major drawback to
perform high substrate concentration lipoxygenation is the optimum pH of the en-
zyme used, which should be as basic as possible.
Lipoxygenases 8- or 12-specific
In relation to human physiological studies, other LOXs of various specificities such
as 8-LOX or 12-LOX versus AA are important enzymes. To the best of our knowl-
edge, and most likely because of the difficulty of collecting sufficient quantities of
such enzymes as well as a lack of equivalent in the vegetal field, no work has yet been
described that is dedicated specifically to the biotechnological production of 8- and
12-HPETE.
16.3.3 Chemical synthesis of conjugated PUFA hydroperoxides
As an alternative method to the enzymatic generation of PUFA-HPODs, such com-
pounds could be generated chemically through auto-oxidation or photo-oxidation of
PUFAs. In these cases, racemic mixtures of all possible HPODs regioisomers are
clearly formed. As shown by Porter et al. (1979) in the photo-oxidation of AA,
the various regioisomers could be separated (though not totally in some cases)
by normal-phase HPLC (order of elution, 12-HPETE, 15- and 14-HPETE, 11-
HPETE, 9-HPETE, 8-HPETE and 5- and 6-HPETE). The reaction could be per-
formed on the millimolar scale (450 mg, 1.48 mg mLâ1) in an organic solvent,
with a yield of HPOD of about 35â40 % (Porter et al., 1979). Although not realized
by Porter et al., it should be mentioned that following the progress made in chiral
HPLC, it may now be possible to separate enantiomers of regioisomerically pure
HPODs. Hence, the combination of chemical methods and HPLC separations might
represent an alternative to a bioconversion for the synthesis of small quantities of
enantiomerically pure PUFA HPODs when the corresponding LOX is not easily
available.
16.3 Substrate and product specificities of lipoxygenases 351
Figure 13. Oxygenation of linoleic anda-linolenic acids by barley seed LOX (Martini et al., 1996b).