Purification and partial characterization of proteinase and α-amylase inhibitors from lesser yam (Dioscorea esculenta)

Abstract

The proteinase and α-amylase isoinhibitors of lesser yam were isolated through TCA precipitation and DEAE cellulose chromatography. The major peak with proteinase inhibitor activity obtained by DEAE-cellulose chromatography was further fractionated to five isoinhibitor fractions with molecular weights 67, 50, 27, 15, and 12 kDa respectively in GPC and PAGE. On the contrary, the major peak with α-amylase inhibitor activity segregated into four isoinhibitors with molecular weights 63, 31, 24, and 16 kDa. Unlike most trypsin inhibitors the lesser yam proteinase inhibitors (LYTI) exhibited proportionate decrease in trypsin inhibition with increase in inhibitor concentration. The inhibitor potential of lesser yam α-amylase inhibitor (LYAI) however, increased with increase in inhibitor concentration. The LYTI was fairly thermostable, retaining 50% activity even after heating for 4 h at 90°C, while the LYAI was much less stable at this temperature. Out of the five fractions of LYTI, isoinhibitors II and IV possessed anti-chymotryptic activity, while isoinhibitors I and V exerted 16 and 25% inhibition of α-amylase respectively. The study showed the existence of bi-functional trypsin/amylase and trypsin/chymotrypsin inhibitors, which also exhibited glycoprotein nature. Although red flour beetle proteases and α-amylases were not inhibited by the LYTI and LYAI, mild inhibition was observed against the respective enzymes of coffee bean weevil, rice weevil, and sweet potato weevil.