科研之友
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摘要
Diabetes is a syndrome of disordered metabolism resulting in abnormally high blood sugar levels (hyperglycemia). The one possibility of lowering postprandial glucose levels is by the inhibition of alpha-amylase activity. In this study, aqueous extracts from local Thai fruits were tested for their inhibitory effect on alpha-amylase. The results showed that the fruits of Kluai Hom Thong; Musa (AAA group) showed significant reduction in alpha-amylase activity. An alpha-amylase inhibitor was purified by using a combination of ammonium sulfate precipitation, ion exchange chromatography with DEAE cellulose, and gel filtration chromatography with Superdex 75, respectively. The enriched preparation had a specific activity of 355.7 AI U/mg proteins for a yield of 18.5% total protein. The molecular weight of this alpha-amylase inhibitor was estimated by SDS-15% (w/v) PAGE to be about similar to 20 kDa. Periodic staining and phenol-sulfuric assay showed that the alpha-amylase inhibitor was a glycoprotein and contained 10.74 +/- 0.35% (by weight) carbohydrate moiety. The pH stability of this alpha-amylase inhibitor was between pH 4 and 7, and it is stable up to 40 degrees C but is totally inactivated after exposure to 40 degrees C for 120 min. The alpha-amylase inhibitory activity was stimulated by Ca2+ and Mn-2 at less than 25 mM but not by Mg2+, Fe3+, Hg2+, Co2+, and EDTA. Determination of the kinetics of the inhibition of alpha-amylase by standard enzymatic methods indicated the K-i of this protein was 0.89 mg protein/mL. The amino acid sequence of an internal fragment of this purified alpha-amylase inhibitor had a similarity to the sequence from the plant lectin/endochitnase1 family.
- 出版日期2012
