Botanical Studies (2008) 49: 101-108.
*
Corresponding author: E-mail: boyhlin@gate.sinica.edu.tw;
Fax: 886-2-2782-7954; Tel: 886-2-2789-9590 ext. 321.
BiochemiStry
Sweet potato storage root trypsin inhibitor and their
peptic hydrolysates exhibited angiotensin converting
enzyme inhibitory activity in vitro
Guan-Jhong HUANG
1
, Yu-Ling HO
2
, Hsien-Jung CHEN
3
, Yuan-Shiun CHANG
1
, Shyh-Shyun
HUANG
1
, Hsin-Jung HUNG
1
, and Yaw-Huei LIN
4,*
1
Institute of Chinese Pharmaceutical Sciences, China Medical University, Taichung 404, Taiwan
2
Department of Nursing, Hung Kuang University, Taichung, 433, Taiwan
3
Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung 804, Taiwan
4
Institute of Plant and Microbial Biology, Academia Sinica, Nankang, Taipei 115, Taiwan
(Received September 11, 2007; Accepted October 26, 2007)
ABStrAct.
Trypsin inhibitor (TI), the root storage protein of sweet potato, was shown by
spectrophotometric methods to inhibit angiotensin converting enzyme (ACE) in a dose-dependent manner
(50-200 £gg/mL, with 31.9-53.2% inhibition) using N-[3-(2-furyl) acryloyl]-Phe-Gly-Gly (FAPGG) as a
substrate. The 50% inhibition (IC
50
) of ACE activity required 187.96ƒn £gg/mL TI compared to 10 nM (868 ng/
mL) of Captopril. The use of TLC also showed TI as ACE inhibitor. TI acted as a mixed type inhibitor against
ACE using FAPGG as a substrate. When 200 £gg/mL TI were added, Vmax and Km were, respectively 0.013
£GA/min and 0.715 mM while without TI they were 0.027 £GA/min and 0.419 mM. Pepsin was used for TI
hydrolysis for different times. ACE inhibitory activity was found to increase from 34% to about 83% after 24
h of hydrolysis. The results suggested that when small peptides increased by pepsin hydrolysis of the TI ACE
inhibitory capacity also increased up to 24 h and then decreased, it may be due to the disappearance of some
conformational requirements. Ten peptides¡Xnamely HDHM, LR, SNIP, VRL, TYCQ, GTEKC, RF, VKAGE,
AH and KIEL¡Xwere synthesized based on the simulated pepsin digestion of trypsin inhibitor and then tested
for ACE inhibitory activity. IC
50
values of individual peptides were 276.2, 746.4, 228.3, 208.6, 2.3, 275.8,
392.2, 141.56, 523.5 and 849.7 £gM, suggesting that TYCQ might represent the main active site for the ACE
inhibition. TI and its hydrolysates might be good for control of hypertension and other diseases when people
consume sweet potato tuberous roots.
Keywords: Angiotensin converting enzyme (ACE); Trypsin inhibitor; Pepsin; Sweet potato.
iNtroDUctioN
Many bioactive peptides have common structural
properties that include a relatively short peptide residue
length (e.g. 2-9 amino acids), possessing hydrophobic
amino acid residues in addition to proline, lysine or
arginine groups. Bioactive peptides are among the many
functional components identified in foods. These are small
protein fragments that have biological effects once they are
released during gastrointestinal digestion in the organism
or by previous in vitro protein hydrolysis. Bioactive
peptides with immunostimulating (Parker et al., 1984; Fiat
et al., 1993), opioid (Zioudrou et al., 1979), antithrombotic
(Scarborough, 1991),
caseino-phosphopeptic (Maubois
and Leonil, 1989),
bactericidal (Bellamy et al., 1993),
antioxidant or angiotensin-converting enzyme inhibitor
(Ehlers and Riordan, 1989) functions have been the
research focus in recent years.
ACE (peptidyldipeptide hydrolyase EC 3.4.15.1) is
a glycoprotein and a dipeptide-liberating exopeptidase
classically associated with the renin-angiotensin system
regulating peripheral blood pressure (Mullally et al.,
1996). ACE removes a dipeptide from the C-terminus of
angiotensin I to form angiotensin II, a very hypertensive
compound. Several endogenous peptides, such as
enkephalins, £]-endorphin, and substance P, were reported
to be competitive substrates and inhibitors of ACE.
Several food-derived peptides from £\-lactoalbumin,
£]-lactoglobulin (Pihlanto-Leppala et al., 1998),
casein
(Maruyama et al., 1987), zein, mucilage (Huang et al.,
2006), and azein (Yano et al., 1996) also inhibited ACE.
Several antioxidant peptides (reduced glutathione and
carnosine-related peptides) (Hou et al., 2003) and synthetic
peptides also exhibited ACE inhibitor activities (Chen et
al., 2003).