Journal of Nutritional Science and Vitaminology
Online ISSN : 1881-7742
Print ISSN : 0301-4800
ISSN-L : 0301-4800
Activity Changes in Cranberry Bean (Phaseolus vulgaris) α-Amylase Inhibitor by Chemical Modification and Enzymatic Digestion
Makoto KOTARUHung-Yu YEHHideki YOSHIKAWATsuneo IKEUCHIKimikazu IWAMIFumio IBUKI
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1989 Volume 35 Issue 1 Pages 71-80

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Abstract

An a-amylase inhibitor was prepared from cranberry bean (Phaseolus vulgaris). The α-amylase inhibitor was composed of three different subunits not linked by disulfide bridges and only one of them contained carbohydrate. Although the inhibitor was stable at pH 3 to 7, it was heat labile at pH 3 and 5. Chemical modification of the amino groups and the guanido groups in cranberry bean a-amylase inhibitor molecule resulted in rapid loss of the inhibitory activity, respectively. Oxidation of the tryptophan residues also led to loss of the activity. On the other hand, reductive methylation of the amino groups scarcely affected the activity. The inhibitor was quite resistant to the proteolytic digestions by pepsin and trypsin, while it was relatively susceptible to the action of chymotrypsin.

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