What occurs during desaturation of fatty acids?
A.
Palmitate and stearate serve as precursors of the two most common monounsaturated fatty acids of animal tissues: palmitoleate, 16:1(Δ 9 ), and oleate, 18:1(Δ 9 ); both of these fatty acids have a single cis double bond between C-9 and C-10.
B.
The double bond is introduced into the fatty acid chain by an oxidative reaction catalyzed by fatty acyl–CoA desaturase, a mixed-function oxidase. Two different substrates, the fatty acid and NADPH, simultaneously undergo twoelectron oxidations.
C.
The path of electron flow includes a cytochrome (cytochrome b 5 ) and a flavoprotein (cytochrome b 5 reductase), both of which, like fatty acyl–CoA desaturase, are in the smooth ER.
D.
In plants, oleate is produced by a stearoyl-ACP desaturase (SCD) that uses reduced ferredoxin as the electron donor in the chloroplast stroma.