Abstract
Valerophenone synthase (VPS) catalyzes the biosynthesis of phlorisovalerophenone, which is a precursor of hop (Humulus lupulus L.) resin. The VPS gene is specifically expressed in the lupulin gland, and the enzyme has a high similarity to chalcone synthase (CHS). CHS catalyzes the formation of naringenin-chalcone; it is considered a precursor of the prenylflavonoids, which accumulate in the lupulin gland. We tried to confirm whether VPS has CHS activity using the purified translation product of the VPS gene expressed in Escherichia coli. The results indicated that VPS had CHS activity and that the enzyme activity of VPS was about six times stronger than the CHS activity. Therefore, VPS seems to contribute to the biosynthesis of both resin and the prenylflavonoids in the lupulin gland, and the difference in the bifunctional activities of VPS might have some effect on the relative amounts of resin and prenylflavonoid in the gland. Furthermore, we investigated (by Southern analysis) the existence of CHS genes, which contribute to the polyphenol biosynthesis in the bract and bracteole. We confirmed that there are two types of VPS genes, and also more than two other types of genes, that have high similarity to the VPS gene and might be the CHS gene.
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