A chimera-like alpha-amylase inhibitor suggesting the evolution of Phaseolus vulgaris alpha-amylase inhibitor.
White kidney bean (Phaseolus vulgaris) contains two kinds of alpha-amylase inhibitors, one heat-stable (alpha AI-s) and one heat-labile (alpha AI-u). alpha AI-s has recently been revealed to be a tetrameric complex, alpha(2)beta(2), with two active sites [Kasahara et al. (1996) J. Biochem. 120, 177-183]. The present study was undertaken to reveal the molecular features of alpha AI-u, which is composed of three kinds of subunits, alpha, beta, and gamma. The gamma-subunit, in contrast to the alpha- and beta-subunits that are indistinguishable from the alpha- and beta-subunits of alpha AI-s, was found to correspond to a subunit of an alpha-amylase inhibitor-like protein, which has been identified as an inactive, evolutionary intermediate between arcelin and the alpha-amylase inhibitor in a P. vulgaris defense protein family. The polypeptide molecular weight of alpha AI-u determined by the light-scattering technique, together with the polypeptide molecular weights of the subunits, suggests that alpha AI-u is a trimeric complex, alpha beta gamma. The inhibition of alpha AI-u by increasing amounts of porcine pancreatic alpha-amylase (PPA) indicates that an inactive 1:1 complex is formed between alpha AI-u and PPA. Molecular weight estimation of the complex by the light-scattering technique confirmed that it is a complex of alpha AI-u with one PPA molecule. Thus it seems probable that alpha AI-u is an evolutionary intermediate of the P. vulgaris alpha-amylase inhibitor.
Wato
S
S
Department of Applied Biological Chemistry, College of Agriculture, Osaka Prefecture University, Gakuen-cho 1-1,Sakai, Osaka 599-8531, Japan.
Kamei
K
K
Arakawa
T
T
Philo
J S
JS
Wen
J
J
Hara
S
S
Yamaguchi
H
H
D000595:Amino Acid Sequence; D019143:Evolution, Molecular; D007887:Fabaceae / Q000737:chemistry*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D010946:Plants, Medicinal; D017386:Sequence Homology, Amino Acid; D014361:Trypsin Inhibitors; D000516:alpha-Amylases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism
D010940:Plant Proteins; D014361:Trypsin Inhibitors; D000516:alpha-Amylases