Probing the Deoxyflavonoid Biosynthesis: Naringenin Chalcone Is a Substrate for the Reductase Synthesizing Isoliquiritigenin.

Isoliquiritigenin formation is a key reaction during deoxyflavonoid biosynthesis, which is catalyzed by two enzymes, chalcone synthase (CHS) and reductase (CHR). The substrates for CHS are established. However, the substrate for CHR is unknown. In this study, an in vitro reaction was performed to confirm whether naringenin chalcone can be a substrate. Naringenin chalcone was used as a substrate during the CHR reaction. Analyzing the product revealed that isoliquiritigenin was produced from naringenin chalcone, indicating that naringenin chalcone is a substrate. This study is the first to identify a substrate for CHR, reveals that deoxyflavonoid biosynthesis diverges from naringenin chalcone, endorses the term "chalcone reductase," and answers the long-standing questions about doubly-labeled acetic acid uptake pattern in deoxyflavonoid biosynthesis.