In contrast to the Cornforth's basic principle for the isoprenoid biosynthesis, we have recently found that the unusual elimination of the pro-4S hydrogen of MVA took place in the formation of the Z-isoprene residue during the biosynthesis of polyprenols, named malloprenols, in Mallotus japonicus. We have now investigated (i) the enzyme system participating in the malloprenol biosynthesis, (ii) the stereochemistry of the hydrogen elimination in the formation of malloprenol with the enzyme system, and (iii) occurrence of the unusual hydrogen elimination in the other species of higher plants. The enzyme system participating in the biosynthesis of malloprenols was purified by fractionation with ammonium sulfate and a DEAE-cellulose column. The enzyme system was found to be different from the system which participates in the biosynthesis of farnesol. Occurrence of the unusual hydrogen elimination in the biosynthesis of the Z-isoprene chain of malloprenols was confirmed by incubating IPP-4-^<14>C, (2S)-2-^3H and its (2R)-2-^3H isomer with the enzyme system. On the other hand, occurrence of such an unusual hydrogen elimination was demonstrated by determination of the ^3H/^<14>C ratio in polyprenols biosynthesized from MVA-2-^<14>C, (4R)-4-^3H and its (4S)-4-^3H isomer with Aleurites cordata, Alnus serrulatoides, Aesculus turbinate, Betula platyphylla, Cleome spinosa, and Triadica sebifera. Consequently, it was suggested that elimination of the pro-4S hydrogen of MVA might be the usual mode in the formation of the Z-isoprene chain of polyprenols in higher plants.
