Amylopectin Synthase of Eimeria tenella: Identification and Kinetic Characterization

ABSTRACT. A soluble enzyme amylopectin synthase (UDP-glucose-α 1,4-glucan α-4-glucosyltransferase) which transfers glucose from uridine 5'-diphosphate glucose (UDP-glucose) to a primer to form α-I,4-glucosyl linkages has been identified in the extracts of unsporulated oocysts of Eimeria tenella . UDP-glucose and not ADP-glucose was the most active glucosyl donor. Corn amylopectin, rabbit liver glycogen, oyster glycogen and corn starch served as primers; the latter two were less efficient. The enzyme has an apparent pH optimum of 7.5 and exhibited typical Michaelis-Menten kinetics with dependence on both the primer and substrate concentrations. The Michaelis constants (Km). with respect to UDP-glucose, was 0.5 mM; and 0.25 mg/ml and 1.25 mg/ml with respect to amylopectin and rabbit liver glycogen. The product formed by the reaction was predominantly a glucan containing α-1,4 linkages. The specificity of the enzyme suggests that this enzyme is similar to glycogen synthase in eukaryotes and has been designated as amylopectin synthase (UDP-glucose-α-1,4-glucosetransferase EC 2.4.1.11).