Starch Hydrolase Inhibitors from Edible Plants - Advances in Food and Nutrition Research - page 122

discomfort of abdomen, and diarrhea. In this context, the side effect of other
a -glucosidase inhibitor is a legitimate concern.

3. AMYLASE INHIBITORS

a -Amylase (1,4- a - D -glucan-glucanohydrolase, EC3.2.1.1) is a
endoglucanase that catalyzes the hydrolysis of the endo a -(1,4) glycosidic
linkages in starch and related polysaccharides. Hydrolysis of starch is first cat-
alyzed by a -amylase present in human saliva followed by pancreatic amylase
in the duodenum. Human pancreatic a -amylase (HPA) is important phar-
macological target for the treatment of type-2 diabetes. However, the
expense of the HPA is relatively high for research purpose. Instead, porcine
pancreas a -amylase (PPA) is used in vitro digestion measurement. PPA is
composed of 496 amino acid residues and shows 83% identity to its human
counterpart HPA ( Pasero, Mazz´i-Pierron, Abadie, Chicheportiche, &
Marchis-Mouren, 1986 ). PPA is an endo-type amylase and it catalyzes
the hydrolysis of internal a -(1,4) glycosidic bonds in amylose and amylopec-
tin through multiple attack toward the nonreducing end ( Robyt & French,
1970 ). The products of hydrolysis of porcine pancreatic a -amylase are
mainly maltose, maltotriose, and maltotetraose ( Yook & Robyt, 2002 ) .
PPA has two isomers PPA isozyme-I (PPA-I) and PPA-II, which have
the same molecular weight but differ slightly in amino acid composition
and isoelectric point ( Pasero et al., 1986 ) .
Naturally occurring a -amylase inhibitors include protein-based ones and
secondary metabolites. The former is out of the scope of this article because
they tend to denature upon thermal or acidic (stomach acidity) treatment
and lose their activity when reaching small intestine. Herein, we summarize
the most recent literatures on a -amylase inhibitors. The methods used in
measuring their inhibition activity are also listed because different methods
may result in different IC 50 values. In comparison with a -glucosidase, lesser
reports are found in a -amylase and most of the studies are on polyphenols.
Isookanin (

)( Fig. 3.8 ) isolated from Spanish needles, Bidens bipinnata ,
was shown moderate inhibition activity on HPA (IC 50 of 0.447 mg/mL or
156 m M) measured using iodometric assay ( Yang et al., 2012 ). It should be
noted that isookanin contains two catecholic units, and thus it is expected to
be a good reductant, which may reduce iodine causing false positive results.
From the leaf of water apply ( Syzygium aqueum ) leaf, myricetin-3- O -
rhamnoside (

57

)( Fig. 3.2 ) were iso-
lated, and the inhibition activity on a -amylase inhibition was measured

9 ) and europetin-3- O -rhamnoside ( 10