Abstract

Recently, we identified an Arabidopsis gene (At1g04010) encoding an enzyme (Phospholipid: Sterol Acyltransferase, PSAT) responsible for most of the sterol ester formation in this plant. The enzyme belongs to the LCAT/PDAT family and is the only intracellular enzyme so far found which catalyses an acyl-CoA independent sterol ester formation. The enzyme utilises phospholipids (preferentially PE) as acyl donors and acylate various sterols and sterol biosynthesis intermediates. The enzyme had poor activity for sterol intermediates compared to end-product sterols when the acyl acceptors were presented as single substrates. However, it had been shown previously that sterol intermediates are preferentially accumulated as esters in plants overproducing sterols. An explanation for these apparent conflicting in-vivo and in-vitro results was given by sterol selectivity experiments. Using RPHPTLC, we were able to separate some of the acylated sterol intermediates from acylated end-product sterols. Competition experiments were performed using sitosterol as an end-product sterol and 24-ethylidene lophenol, cycloartenol or obtusifoliol as intermediate. When the sterol intermediates were used as single substrate, the PSAT activity was less than half that of sitosterol. However, when they were presented to the enzyme together with sitosterol, the acylation of sitosterol was drastically decreased and the acylation rates of the intermediates increased up to 3-fold. Based on these results we conclude that PSAT is activated by the end-product sterols and that the activated PSAT has selectivity towards sterol intermediates. In this way, PSAT can both regulate the pool size of free sterols as well as limit the amount of free sterol intermediates in the membranes

Keywords

Sterol

Published in

Publisher: Euro Fed Lipid e.V

Conference

2nd European Symposium on Plant Lipids

SLU Authors

• Carlsson, Anders

  • Department of Crop Science, Swedish University of Agricultural Sciences
    

• Stymne, Sten

  • Department of Crop Science, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Agricultural Science
Food Science


Permanent link to this page (URI)

https://res.slu.se/id/publ/6747