Palmitoleate formation by soybean stearoyl-acyl carrier protein desaturase

Palmitoyl (hexadecanoyl)-acyl carrier protein (ACP) was found to be an alternate substrate for recombinant soybean stearoyl (octadecanoyl)-ACP delta 9-desaturase. The fatty acid product was identified as palmitoleic acid ((Z)-hexadec-9-enoic acid), which suggests that the locus of desaturation was fixed with respect to the carboxyl, not methyl, end of each substrate acyl group. The apparent specificity factor (Vmax/Km) of the desaturase for stearoyl-ACP was > 100-fold larger than for palmitoyl-ACP, mostly because of the difference in Vmax for the two substrates.