Journal
JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY
Volume 57, Issue 19, Pages 9218-9225Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jf9017383
Keywords
alpha-Amylase inhibitor; caffeic acid; chlorogenic acid; enzyme kinetics; mixed-type inhibition
Funding
- Japan Society for the Promotion of Science [17380065, 20380061]
- Grants-in-Aid for Scientific Research [17380065] Funding Source: KAKEN
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Chlorogenic acid (5-caffeoylquinic acid, 5-CQA) is a kind of polyphenol and is richly included in green coffee beans. The inhibitory effects of 5-CQA and its components, caffeic acid (CA) and quinic acid (QA), on the two porcine pancreas (alpha-amylase (PPA) isozymes, PPA-I and PPA-II, were investigated using p-nitrophenyl-alpha-D-maltoside as substrate at pH 6.9 and 30 degrees C. The inhibition potencies of the respective inhibitors against both PPA isozymes were almost the same and in the order of 5-CQA > CA >> QA. Their IC50 values were 0.07-0.08 mM, 0.37-0.40 mM, and 25.3-26.5 mM, respectively. The inhibition mechanisms of 5-CQA and CA were investigated by kinetic analyses, and the inhibitor constants K-i and K-i' (for the free enzyme and enzyme-substrate complex, respectively) were determined. It was indicated that 5-CQA and CA showed mixed-type inhibition with Ki > Ki' against both PPA-I and PPA-II. The binding of PPA-I or PPA-II with 5-CQA or CA was all exothermic and enthalpy-driven. CIA is a poor inhibitor, and its inhibitory mode was unique and hardly analyzed by a simple Michaelis-Menten-type interaction between the enzyme and inhibitor. However, it was shown that the inhibitory activity of CA was enhanced 5 times by ester-bond formation with QA in the form of 5-CQA. These results provide us with significant hints for the development of alpha-amylase inhibitors useful for the prevention of diabetes and obesity.
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