PLANT PHYSIOLOGY , Vol 102, Issue 4 1275-1278, Copyright © 1993 by American Society of Plant Biologists
|
METABOLISM AND ENZYMOLOGY |
An in Vivo Study of Substrate Specificities of Acyl-Lipid Desaturases and Acyltransferases in Lipid Synthesis in Synechocystis PCC6803
S. Higashi and N. Murata
National Institute for Basic Biology, Myodaiji, Okazaki 444, Japan
The cyanobacterium Synechocystis PCC6803 was fed heptanoic acid to study
the substrate specificities of desaturases and acyltransferases in lipid
synthesis. This aliphatic acid was elongated to C15, C17, and C19 fatty
acids, which were incorporated into polar glycerolipids and desaturated.
The double bonds were located at the [delta]6, [delta]9, [delta]12, and
[omega]3 positions of the fatty acids. This suggests that the [delta]9
desaturase counts the carbon number from the carboxy terminus, whereas the
so-called [delta]15 desaturase counts from the methyl terminus. The
counting mechanisms of the [delta]6 and [delta]12 desaturases are not fully
understood. In the distribution of fatty acids at the sn positions of the
glycerol moiety, the C17, C18, and C19 fatty acids were located at the sn-1
position, whereas the C15 and C16 fatty acids were located at the sn-2
position. This suggests that glycerol-3-phosphate acyltransferase
specifically transfers heptadecanoic, octadecanoic, and nonadecanoic acids,
whereas 1-acylglycerol-3-phosphate acyltransferase specifically transfers
pentadecanoic and hexadecanoic acids.
