Induction and Characterization of a NADPH-Dependent Flavone Synthase from Cell Cultures of Soybean

Abstract

Microsomal preparations from osmotically stressed soybean cells catalyze the conversion of (2S)-naringenin to apigenin in presence of NADPH. In contrast, such preparations from normal soybean cells or from elicitor-challenged cells catalyze the conversion of (2S)-naringenin to genistein (isoflavone synthase). It is concluded that osmotic stress of the cells causes a switch from isoflavone to flavone synthesis. The flavone synthase from osmotically stressed cells corresponds in its properties to the microsomal flavone synthase found in several flowers (G. Stotz and G. Forkmann, Z. Naturforsch. 36c, 737-741 (1981)) and differs from the flavone synthase I from parsley cell cultures which is a soluble Fe2+ and 2-oxoglutarate dependent dioxygenase. Flavone synthase II from soybean has an absolute requirement for NADPH and oxygen. It is inhibited by carbon monoxide in presence of oxygen and this inhibition is reversed by light. It is also inhibited by cytochrome c and by a number of cytochrome P-450 inhibitors. This and other properties show that flavone synthase II is a cytochrome P-450 dependent monooxygenase.