The reduction of geraniol to citronellol is the first step for the synthesis of natural phytol in the production of tocopherols and natural vitamin K.Baker's yeast was used in the bioreduction described above as a whole-cell biocatalyst.However,the enzyme responsible for the reduction of geraniol to citronellol is not yet known.Four old yellow enzyme(OYE)genes were cloned from yeast and plants,and expressed in Escherichia coli for a high level of recombinant proteins.The recombinant protein displayed a catalytic activity of converting geraniol to citronellol as a sole product verified by GC-MS analyses.The recombinant OYE2 intact cells were found to show 3.7 and 1.9-fold higher activity than that of yeast cells and the recombinant crude extracts,respectively.Compared to the recombinant fusion enzyme,the entrokinase-cleaved enzyme displayed nearly identical activity for geraniol reduction.To our knowledge,this is the first enzyme identified to catalyze the formation of citronellol from geraniol by reducing the allylic alcohol double bond,which is normally known as inactivating group for the old yellow enzymes.
Tian-Tian YUANQian-Qian CHENPei-Ji ZHAOYing ZENGXiao-Zhu LIUShan LU
