PLANT PHYSIOLOGY , Vol 104, Issue 3 839-844, Copyright © 1994 by American Society of Plant Biologists
|
METABOLISM AND ENZYMOLOGY |
Specificities of the Acyl-Acyl Carrier Protein (ACP) Thioesterase and Glycerol-3-Phosphate Acyltransferase for Octadecenoyl-ACP Isomers (Identification of a Petroselinoyl-ACP Thioesterase in Umbelliferae)
P. Dormann, M. Frentzen and J. B. Ohlrogge
Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824-1312 (P.D., J.B.O.)
This study was designed to address the question: How specific for double
bond position and conformation are plant enzymes that act on oleoyl-acyl
carrier protein (ACP)? Octadecenoyl-ACPs with cis double bonds at positions
[delta]6, [delta]7, [delta]8, [delta]9, [delta]10, [delta]11, or [delta]12
and elaidyl (18:1[delta]9trans)-ACP were synthesized and used to
characterize the substrate specificity of the acyl-ACP thioesterase and
acyl-ACP:sn-glycerol-3-phosphate acyltransferase. The two enzymes were
found to be specific for the [delta]9 position of the double bond. The
thioesterase was highly specific for the [delta]9 cis conformation, but the
transferase was almost equally active with the cis and the trans isomer of
18:1[delta]9-ACP. In plants such as the Umbelliferae species coriander
(Coriandrum sativum L.) that accumulate petroselinic acid (18:1[delta]6cis)
in their seed triacylglycerols, a high petroselinoyl-ACP thioesterase
activity was found in addition to the oleoyl-ACP thioesterase. The two
activities could be separated by anion-exchange chromatography, indicating
that the petroselinoyl-ACP thioesterase is represented by a distinct
polypeptide.
