An endogenous alpha-amylase inhibitor in barley kernels.

Barley (Hordeum distichum cv Klages) kernels were shown to contain a factor that converted malted barley alpha-amylase II to the alpha-amylase III form. After purification by ammonium sulfate fractionation, ion exchange chromatography on DEAE-Sephacel, and gel-filtration on Bio Gel P60, the factor gave a single band of protein on isoelectric focusing. The purified factor inhibited hydrolysis of soluble starch by alpha-amylase II from malted barley and germinated wheat (Triticum aestivum cv Neepawa). However, alpha-amylase I from these cereals was not affected. The inhibitor was not dialyzable and was retained by a PM 10 ultrafiltration membrane suggesting a molecular weight greater than 10,000 daltons. Heat treatment of the inhibitor at 70 degrees C for 15 minutes at pH 5.5 and 8.0 resulted in considerable loss of inhibitory activity.