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PLANT PHYSIOLOGY , Vol 109, Issue 2 707-716, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Fatty Acid-Elongating Activity in Rapidly Expanding Leek Epidermis
K. J. Evenson and D. Post-Beittenmiller
Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73402
A microsomal fatty acid elongase activity measured in epidermis of rapidly
expanding leek (Allium porrum L.) was 10-fold higher in specific activity
than preparations from store-bought leek. These preparations elongated acyl
chains effectively using endogenous or supplied primers. Elongation of
C20:0 was specifically inhibited by 2 [mu]M cerulenin, and labeling
experiments with [3H]cerulenin labeled two polypeptides (65 and 88 kD). ATP
was required for maximal elongase activity in expanding leaves but was lost
in nonexpanding tissues. Both [14C]stearoyl-coenzyme A (CoA) and
[14C]stearate were maximally elongated in the presence of ATP. Addition of
fully reduced CoA, however, inhibited [14C]stearate elongation, suggesting
that stearoyl-CoA synthesis was not a prerequisite for elongation.
Furthermore, microsomes preincubated with [14C]stearoyl-CoA plus ATP
resulted in loss of radiolabel from the acyl-CoA pool without a
corresponding loss in elongating activity. The lack of correlation between
elongating activity and the label retained in the putative acyl-CoA
substrate pool suggests that acyl-CoAs may not be the immediate precursors
for elongation and that ATP plays a critical, yet undefined, role in the
elongation process. We propose that an ATP-dependent elongating activity
may generate the long-chain fatty acids required for wax biosynthesis.
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