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a -amylase and a -glucosidase activity ( Kelemen &Whelan, 1966 ) . Recently,
we have developed a high-throughput assay based on monitoring turbidity
changes during starch hydrolysis for quantification of starch hydrolase (both
a -amylase and a -glucosidase) inhibition activity ( Liu, Song, Wang, &
Huang, 2011 ) . This assay directly measures the enzyme activity with native
substrates and avoids potential interferences.
While methods used in measuring the inhibitory activity are important
factors in examining the literature, the source of enzymes used is equally crit-
ical. It is known that microbial and mammal amylases have significantly dif-
ferent structures that have a great impact on their response to inhibitors
( Cuyvers, Dornez, Delcour, & Courtin, 2012 ). To be of relevancy to
humans, it is advisable to use porcine pancreatic juice and a -glucosidase
from rat intestine if not human counterparts.
2. a -GLUCOSIDASE INHIBITORS FROM
BOTANICAL SOURCES
2.1. Glycomimetics
a -Glucosidase and a -amylase hydrolyze glycosidic bonds via conjugated
acid (R d CO 2 H) and base (R d CO 2 ) mechanism. The enzymes bind
the substrate primarily through hydrogen bonds. Hence, glycomimetics
with structural similarity to a -glucosidase substrate (maltose and oligosac-
charides) but bearing a positive charge near the glycosidic bond is a good
competitive inhibitor as the glycomimetics molecule binds to the enzyme
active center through charge interactions with the catalytic group in addi-
tion to hydrogen bonds. Such inhibitors include some well-known and
commercialized molecules such as acarbose, miglitol, and voglibose
( Etxeberria, de la Garza, Campion, Martinez, & Milagro, 2012 ) .
In addition, sulfonium ion-containing glycomimetics, neoponkoranol iso-
lated from the stems of Salacia chinensis ( Xie et al., 2011 ) showed potent
inhibitory activity against rat intestinal maltase, sucrase, and isomaltase with
IC 50 values of 5.1, 1, and 1.4 m M, respectively. This type of inhibitors
have been reviewed previously and thus not repeated here ( Ernst &
Magnani, 2009 ) .
2.2. Polyphenols
2.2.1 Tannins
Perhaps polyphenolic compounds are one of the most intensively studied
natural products for their activity as radical scavengers, anti-inflammatory
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