KAS III (Jaworski et al., 1989). A second condensing enzyme,
KAS I, is believed responsible for producing chain lengths from
six to 16 carbons. Finally, elongation of the 16carbon palmitoyl-
ACP to stearoyl-ACP requires a separate condensing enzyme,
KAS II. The initial product of each condensation reaction is
a 3-ketoacyl-ACP. Three additional reactions occur after each
condensation to form a saturated fatty acid (Figure 3). The
3-ketoacyl-ACP is reduced at the carbonyl group by the enzyme
3-ketoacyl-ACP reductase, which uses NADPH as the
electron donor. The next reaction is dehydration by hydroxyacyl-
ACP dehydratase. Each round of fatty acid synthesis is then
completed by the enzyme enoyl-ACP reductase, which uses
NADH or NADPH to reduce the trans-2 double bond to form
a saturated fatty acid. The combined action of these four reactions
leads to the lengthening of the precursor fatty acid by
two carbons while it is still attached to ACP as a thioester