Mechanism of fatty acid desaturation in the green alga Chlorella vulgaris.
The hypothesis that the Delta9 desaturase of Chlorella vulgaris might operate by a synchronous mechanism has been tested using a kinetic isotope effect (KIE) approach. Thus the intermolecular primary deuterium KIE on the individual C-H bond cleavage steps involved in Delta9 desaturation have been determined by incubating growing cultures of C. vulgaris (strain 211/8K) with mixtures of the appropriate regiospecifically deuterated fatty acid analogues. Our analysis shows that the introduction of a double bond between C-9 and C-10 occurs in two discrete steps as the cleavage of the C9-H bond is very sensitive to isotopic substitution (kH/kD = 6.6 +/- 0.3) whereas a negligible isotope effect (kH/kD = 1.05 +/- 0.05) was observed for the C10-H bond-breaking step. Similar results were obtained for linoleic acid biosynthesis (Delta12 desaturation). These data clearly rule out a synchronous mechanism for these reactions.
Behrouzian
B
B
Ottawa-Carleton Chemistry Institute, Department of Chemistry, Carleton University, Ottawa, Ontario, Canada.
Fauconnot
L
L
Daligault
F
F
Nugier-Chauvin
C
C
Patin
H
H
Buist
P H
PH
D002708:Chlorella / Q000201:enzymology*; D044943:Fatty Acid Desaturases / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry
D005227:Fatty Acids; D044943:Fatty Acid Desaturases