**4. Materials and methods**

**Chemicals.** A series of alkyl protocatechuates was available from our previous study [17].

**Enzyme Assay.** The assay was performed as previously reported [11]. The soybean lipox‐ ygenase 1 (EC 1.13.11.12, Type I) used for the bioassay was purchased from Sigma Chemical Co. Linoleic acid (**30**) was used as a substrate. The reaction mixture consisted of 1.2 mM linoleic acid (**30**), 60 mM phosphate buffer (pH 7.0) and different concentra‐ tions of sample. At zero time, the enzyme solution (100 units) was added to the reaction mixture. The lipoxygenase activity was measured polarographically with an oxygen elec‐ trode(YSI 53, Yellow Springs Instrument Co., Yellow Springs, OH) at 25 °C. Calibration of a Clark-type oxygen electrode was performed by using 4-tert-butylcatechol.The native enzyme is quite capable of producing 13-HPOD (**27**) directly from linoleic acid (**30**) with‐ out any prior activation.
