The biosynthesis of isoflavonoids was investigated at the enzyme level with elicitor-treated cell suspension cultures of Pueraria Iobata Ohwi (Leguminosae). Our interests were focused mainly on two enzymatic reactions catalyzed by isoflavone synthase (IS) and deoxychalcone synthase (DOCS). IS catalizes the 1,2-aryl migration of B ring, and DOCS achieves the condensation and the reduction during the construction of aromatic A ring. The deoxy type flavanone(2a) and chalcone(1a) were both converted into the corresponding isoflavone(3a) by a microsomal preparation containing chalcone-flavanone isomerase. Competitive experiments with [^3H]flavanone and [^<14>C]chalcone revealed that flavanone is the true substrate of IS. IS reaction required NADPH and O_2 and was inhibited by CO gas or SKF525A. These observations suggest that IS is an enzyme belonging to P-450. DOCS system in P. lobata was partially purified and revealed to be composed of two separate enzymes, chalcone synthase and coacting reductase. DOCS is a new type of polyketide synthase which affords a deoxy-type compound in the presence of NADPH and a hydroxy-type compound in the absence of NADPH.
