CBlock Clinical Studies

July 1, 2000

A chimera-like alpha-amylase inhibitor suggesting the evolution of Phaseolus vulgaris alpha-amylase inhibitor.

Wato, S.; Kamei, K.; Arakawa, T.; Philo, J.S.; Wen, J.; Hara, S.; Yamaguchi, H.

Journal of J Biochem (Tokyo), Vol. 128
July 1, 2000

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 active, evolutionary intermediate between arcelin and the alpha-amylase inhibitor in a P. vulgaris defense protein family. The polypeptide molecular weight of the alpha AI-u determined by the light-scattering technique, together with the polypetide molecular weights of the subunits, suggests that alpha AI-u is a trimetric 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 probably that alpha AI-u is an evolutionary intermediate of the P. vulgaris alpha-amylase inhibitor.