Molecular properties of the enzymic phytohemagglutinin of mung bean

Mung bean seeds possess a tetrameric galactose-binding protein that displays two types of activities: (a) a hemagglutinin activity, and (b) an alpha-galactosidase activity. This protein can be reversibly converted by pH changes from a tetrameric form, which possesses both enzymic and hemagglutinin a...

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Bibliographic Details
Published in:The Journal of biological chemistry 1981-07, Vol.256 (14), p.7177-7180
Main Authors: del Campillo, E, Shannon, L M, Hankins, C N
Format: Article
Language:English
Subjects:
alpha-Galactosidase - metabolism
Calcium-Binding Proteins
Carbohydrates
Carrier Proteins - analysis
Chemotaxis
Circular Dichroism
Galactose - analysis
Hemagglutination
Kinetics
Macromolecular Substances
Molecular Weight
Monosaccharide Transport Proteins
Periplasmic Binding Proteins
Phytohemagglutinins
Plant Lectins
Protein Conformation
Seeds - enzymology
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Summary:Mung bean seeds possess a tetrameric galactose-binding protein that displays two types of activities: (a) a hemagglutinin activity, and (b) an alpha-galactosidase activity. This protein can be reversibly converted by pH changes from a tetrameric form, which possesses both enzymic and hemagglutinin activities, to a monomeric form which possesses enzymic activity only. This observation suggests that the enzymic phytohemagglutinin is an aggregated form of a monomeric alpha-galactosidase. The tetrameric alpha-galactosidase has a pH optimum of about pH 7.0, while the monomeric form displays a pH optimum of 5.6. Circular dichroism difference spectra and inhibition studies suggest that aggregation induces conformational changes in the subunits sufficient to alter their enzymatic properties. The possibility of in vivo changes in subunit equilibria, when combined with the accompanying alterations in activity, provides a new concept worthy of consideration with respect to the physiological role of phytohemagglutinins.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(19)68944-1