Estimation of the Mutation Site of a Soyasapogenol A-Deficient Soybean [Glycine max (L.) Merr.] by LC-MS/MS Profile Analysis

Worldwide attention toward the health benefits from soybean saponins has increased and they have also attracted attention in addressing taste characteristics. There are two soybean saponin aglycons: soyasapogenol A (SA), which causes a bitter astringent taste; and DDMP-conjugated soyasapogenol B (SB), which has health benefits. SA-deficient mutant soybean (Tohoku No. 152) that could have better taste was recently developed. However, the mutation site is unknown therefore undesirable components may accumulate and decrease its food value. Soyasapogenols are thought to be synthesized from 2,3 -oxidosqualene through β-amyrin and hydroxylated by cytochrome P450 family enzymes. If the SA-deficiency were caused by enzyme elimination, intermediate components could accumulate in the mutant seeds. We used LC-MS/MS profile analysis to investigate accumulation of SA precursor components in Tohoku No. 152, but none was detected. We deduced that the SA-deficient mutant eliminates the P450 monooxygenase that hydroxylates the C -21 position of the SA precursor component. SA-deficiency resulted in an increase of DDMP-saponin content.