supplementary material is available for this article at 10.1007/s13659 - 011 - 0032 - 6 and is accessible for authorized users .
 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 . 
 electronic supplementary materialsupplementary material is available for this article at 10.1007/s13659 - 011 - 0032 - 6 and is accessible for authorized users . 
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