The optimization of the expression of recombinant 6-His-tagged HPO lyase in Yarrowia lipolytica is described: 1800 U/L of culture was detected at 24 h of culture on a medium containing olive oil as the sole carbon source. The enzyme was purified by IMAC and showed an optimal pH at 5.5, an optimal temperature at 20 degrees C and a K-m value of 9 mu M with 13-HPOD substrate. The participation of radicals during the catalysis of purified bell pepper fruit hydfoperoxide lyase has been observed by electron paramagnetic resonance spectroscopy and the yet unidentified radical species might be an alkyl or alkoxyl radical linked to the enzyme. (c) 2006 Elsevier Inc. All rights reserved.