Purification and Characterisation of Limit Dextrinase Inhibitors from Barley

Two inhibitors of malt limit dextrinase were purified from a crude barley extract (cv. Harrington) by CM cellulose ion exchange chromatography and chromatofocusing. The inhibitors were heat-stable proteins of M r approximately 15k and isoelectric points of 6·7 (low pI inhibitor) and 7·2 (high pI inhibitor). Both inhibitors were active over a wide pH range, and were most effective at pH 5·5 to 6·5, the pH optimum of the limit dextrinase enzyme. Inactivation of the limit dextrinase enzyme by either inhibitor could be reversed by warning the complex at 40°C in the presence of reducing agents.