Purification, immobilization and characterization of linoleic acid isomerase on modified palygorskite

Linoleic acid isomerase from Lactobacillus delbrueckii subsp. bulgaricus 1.1480 was purified by DEAE ion-exchange chromatography and gel filtration chromatography. An overall 5.1% yield and purification of 93-fold were obtained. The molecular weight of the purified protein was ~41 kDa which was analyzed by SDS-PAGE. The purified enzyme was immobilized on palygorskite modified with 3-aminopropyltriethoxysilane. The immobilized enzyme showed an activity of 82 U/g. The optimal temperature and pH for the activity of the free enzyme were 30 °C and pH 6.5, respectively; whereas those for the immobilized enzyme were 35 °C and pH 7.0, respectively. The immobilized enzyme was more stable than the free enzyme at 30-60 °C, and the operational stability result showed that more than 85% of its initial activity was retained after incubation for 3 h. The K (m) and V (max) values of the immobilized enzyme were found to be 0.0619 mmol l(-1) and 0.147 mmol h(-1) mg(-1), respectively. The immobilized enzyme had high operational stability and retained high enzymatic activity after seven cycles of reuse at 37 °C.