Influence of Carboxylic Acids on Wheat CarboxypeptidaseTheir Inhibition Modes and Effect of Citric Acid on Stabilization in Spray Drying

Abstract

Spray drying was investigated as one of the drying methods expected to be useful for the production of powdered wheat carboxypeptidase. Heat stability test revealed that crude enzyme preparation was stable up to 50°C for 45min. Recrystallized enzyme was in hibited by oxalic acid, succinic acid, malic acid, citric acid, and maleic acid at conce ntrations of 10 mM and 50mM. Tartaric acid and fumaric acid did not inhibit the enzyme. The inhibition type and the K_i value for di- and tri-carboxylic acids, which acted as an inhibitor for the enzyme, were examined. Oxalic acid, malic acid, and maleic acid served as a noncompetitive inhibitor and their K_i values were 7.0, 12, and 24mM, respectively. Succinic acid was an inhibitor of mixed type and its K_i value, 10mM. Citric acid showed a competitive inhibition and the smallest K_i value, 4.4mM, among the inhibitors tested. The enzyme extracted with 0.04M citric acid solution was spray-dried in a yield of 100%.