Abstract
The structure and stability of four α-amylase inhibitors (TAI, UAI, MAI-2 and SAI-2) from Toramame (Phaseolus vulgaris L.), Uzuramame (Phaseolus vulgaris L.), Murasakihanamame (Phaseolus coccineus L.) and Shirohanamame (Phaseolus coccineus L.) were examined. The amino acid sequence of SAI-2 was the same as the known sequence for MAI-2, but was slightly different from that of TAI and UAI. The sugar chain composition of SAI-2 was remarkably different from that of MAI-2. Thermal stability at pH 5.0, 70°C indicated that SAI-2 and MAI-2 have markedly similar stabilities. Likewise, TAI and UAI, which also had identical amino acid sequences, exhibited markedly similar stabilities.
However, SAI-2 and MAI-2 were more stable than TAI and UAI. These results suggest that thermal stability of α-amylase inhibitors depends on a few amino acid substitutions in their primary structures.
