Association properties of trypsin inhibitors from lima bean.

The molecular-weight properties of three purified proteinase inhibitors from lima bean were studied by using high speed sedimentation equilibrium. Two isoinhibitors [fraction I and II, nomenclature from Jones et al., (18)]do not self-associate at moderate pH and concentration (<4 g/liter). Fraction IV exists as a monomer at pH 2.0 and polymerizes at higher pH values. The molecular-weight data fit a monomer ⇄ dimer equilibrium at pH 7.0, and a monomer ⇄ dimer ⇄ trimer equilibrium at pH 4.65.