Wf. Nieuwenhuizen et al., LIPOXYGENASE IS IRREVERSIBLY INACTIVATED BY THE HYDROPEROXIDES FORMEDFROM THE ENYNOIC ANALOGS OF LINOLEIC-ACID, Biochemistry, 36(15), 1997, pp. 4480-4488
Triple bond analogues of natural fatty acids irreversibly inactivate l
ipoxygenase during their enzymatic conversion [Nieuwenhuizen, W. F., e
t al. (1995) Biochemistry 34, 10538-10545]. To gain insight into the m
echanism of the irreversible inactivation of soybean lipoxygenase-l, w
e studied the enzymatic conversion of two linoleic acid analogues, 9(Z
)-octadec-9-en-12-ynoic acid (9-ODEYA) and 12(Z)-octadec-12-en-9-ynoic
acid (12-ODEYA). During the inactivation process, Fe(III)-lipoxygenas
e converts 9-ODEYA into three products, i.e. 11-oxooctadec-9-en-12-yno
ic acid, racemic 9-hydroxy-10(E)-octadec-10 -en-12-ynoic acid, and rac
emic 9-hydroperoxy-10(E)-octadec-10-en-12-ynoic acid. Fe(II)lipoxygena
se does not convert the inhibitor and is not inactivated by 9-ODEYA. F
e(III)-lipoxygenase converts 12-ODEYA into 13-hydroperoxy-11(Z)-octade
c-11-en-9-ynoic acid (34/66 R/S), 13-hydroperoxy-11(E)-octadec-11-en-9
-ynoic acid (36/64 R/S), 11-hydroperoxyoctadec-12-en-9-ynoic acid (11-
HP-12-ODEYA, enantiomeric composition of 33/67), and 11-oxooctadec-12-
en-9-ynoic acid (11-oxo-12-ODEYA) during the inactivation process. Als
o, Fe(II)-lipoxygenase is inactivated by 12-ODEYA. It converts the inh
ibitor into the same products as Fe(III)-lipoxygenase does, but two ad
ditional products are formed, viz. 13-oxo-11(E)-octadec-11-en-9-ynoic
acid and 13-oxo-11(Z)-octadec-11-en-9-ynoic acid. The purified reactio
n products were tested for their lipoxygenase inhibitory activities. T
he oxo compounds, formed in the reaction of 9-ODEYA and 12-ODEYA, do n
ot inhibit Fe(II)- or Fe(III)-lipoxygenase. The 9- and 13-hydroperoxid
e products that are formed from 9-ODEYA and 12-ODEYA, respectively, ox
idize Fe(II)lipoxygenase to its Fe(III) state and are weak lipoxygenas
e inhibitors. 11-HP-12-ODEYA is, however, the most powerful inhibitor
and is able to oxidize Fe(II)-lipoxygenase to Fe(III)-lipoxygenase. 11
-HP-12-ODEYA is converted into 11-oxo-12-ODEYA by Fe(III)-lipoxygenase
. We propose a mechanism for the latter reaction in which Fe(III)-lipo
xygenase abstracts the bisallylic hydrogen H-11 from 11-HP-12-ODEYA, y
ielding a hydroperoxyl radical which is subsequently cleaved into 11-o
xo-ODEYA and a hydroxyl radical which may inactivate the enzyme.