Ml. Wise et al., BIOSYNTHESIS OF CONJUGATED TRIENE-CONTAINING FATTY-ACIDS BY A NOVEL ISOMERASE FROM THE RED MARINE ALGA PTILOTA-FILICINA, Biochemistry, 33(51), 1994, pp. 15223-15232
The biosynthesis of conjugated triene-containing fatty acids by the re
d alga Ptilota filicina is catalyzed by a novel enzyme, polyenoic fatt
y acid isomerase. The enzyme has been highly purified and is described
here for the first time. Matrix-assisted laser-induced desorption mas
s spectrometry was used to determine that the major protein in the pur
ified enzyme is composed of similar or identical subunits of M(r) 58 1
19 Da. The native enzyme emerges with an apparent M(r) of 174 000 Da f
rom a gel permeation chromatography column. While this enzyme catalyze
s the formation of conjugated trienes from a variety of polyunsaturate
d fatty acid precursors [arachidonate ((5Z,8Z,11Z,14Z)-eicosatetraenoa
te) is converted to (5Z,7E,9E,14Z)-eicosatetraenoate; gamma-linolenate
((6Z,9Z,12Z)-octadecatrienoate) is converted to 6Z,8E,-10E-octadecatr
ienoate], this occurs most rapidly with eicosapentaenoate [(5Z,7E,9E,1
4Z,17Z)-eicosapentaenoate], which is likely the native substrate. Thro
ugh a series of experiments utilizing gamma-linolenates stereospecific
ally labeled with deuterium, we have determined that the enzyme intram
olecularly transfers the bis-allylic pro-S hydrogen from the C11 posit
ion to the C13 position. Furthermore, the bis-allylic pro-R hydrogen a
t C8 in gamma-linolenate is lost to the solvent. Using arachidonate as
substrate, we demonstrated that the C11 olefinic position becomes pro
tonated by a solvent-derived proton. There appears to be no requiremen
t for molecular oxygen, and the transformation is catalyzed by this si
ngle enzyme.