Identification of soybean protein components that modulate the action of insulin in vitro

We have reported that a 37-kDa protein from a soybean isolate shows an affinity for bile acids and modulates insulin action on fat decomposition in vitro [Makino et al., Agric. Biol. Chem., 52, 803 (1988)]. In this study, the major components of the protein were identified as the acidic A1a and A2 subunits of glycinin, via amino-terminal sequence analyses of purified proteins and examination of their effects on fat decomposition in rat adipose cells. The most hydrophobic region of the subunits was found to be responsible for the bile acid-binding ability, and the binding region probably does not contribute to the insulin-modulating activity. These bile acid-binding and insulin-modulating properties were also noted in a 40-kDa protein from pea seeds, probably acidic subunits of legumin, suggesting that these characteristics may be common to legume proteins.