Further characterization studies of the alpha-amylase protein inhibitor of gel electrophoretic mobility 0.19 from the wheat kernel

Abstract

A highly purified amylase protein inhibitor from the kernels of hexaplois wheat, designated 0.19 according to its gel electrophoretic mobility, has been characterized according to its circular dichroism spectra determined at different pH values and in the presence or absence of dissociating and reducing agents. The 0.19 albumin has also been characterized according to the specificity with which it inhibits 21 alpha-amylases from different origins and according to its sensitivity to a number of chemical and enzymatic treatments of its inhibitory action on human saliva and Tenebrio molitor L. larval midgut alpha-amylases. Inhibitory activity of 0.19 toward human saliva amylase significantly increased when the inhibitor was incubated with the enzyme before the addition of starch, but it was not affected by the preincubation of 0.19 with starch. Maltose reversed the inhibition of human saliva by 0.19 and showed some inhibitory activity toward the enzyme. However, maltose concentrations that only slightly affected amylase activity were very effective in restoring the amylase activity inhibited by 0.19. The inhibitory action of 0.19 on human saliva and T. molitor L. amylases were equally resistant to trypsin and thermal treatments, but 0.19 was readily inactivated by incubation with pepsin or by reduction of disulfide bonds. The inhibition of the mammalian amylase by 0.19 was adversely affected by a treatment with CNBr (1:100 ratio of methionine residues to CNBr) whereas the inhibition of the insect amylase was not. As shown by circular dichroism measurements in the far ultraviolet, 0.19 is a protein with about 50% of ordered structure. Significant and largely reversible changes have been observed in the aromatic CD spectrum of 0.19 at alkaline pH values or in the presence of sodium dodecyl sulfate. These changes, which were associated with a partial loss of inhibitory activity, indicate that ionizable tyrosine groups contribute significantly to the ellipticity bands of 0.19 in the near ultraviolet.