Amylopectin synthase of Eimeria tenella: identification and kinetic characterization.
A soluble enzyme amylopectin synthase (UDP-glucose-alpha 1,4-glucan alpha-4-glucosyltransferase) which transfers glucose from uridine 5'-diphosphate glucose (UDP-glucose) to a primer to form alpha-1,4-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 alpha-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-alpha-1,4-glucosetransferase EC 2.4.1.11).
Karkhanis
Y D
YD
Department of Biochemical Parasitology, Merck Research Laboratories, Rahway, New Jersey 07065-0900.
Allocco
J J
JJ
Schmatz
D M
DM
D000687:Amylopectin / Q000096:biosynthesis*; D000818:Animals; D002645:Chickens; D016786:Eimeria tenella / Q000201:enzymology*; D005947:Glucose / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011817:Rabbits; D013379:Substrate Specificity; D013696:Temperature; D014675:Vegetables
D000687:Amylopectin; C083551:amylopectin synthase; D006006:Glycogen Synthase; D005947:Glucose