Assuntos
Glicogênio Sintase/análise , Fígado/enzimologia , Animais , Glucofosfatos , Técnicas In Vitro , Cinética , Masculino , Métodos , Fosforilação , RatosAssuntos
Glicogênio Sintase/metabolismo , Músculos/enzimologia , Animais , Glicogênio , Cinética , Coelhos , Fatores de TempoRESUMO
Using the I form of rabbit muscle glycogen synthase essentially free of glycogen, the kinetics and mechanism of action was investigated. No evidence for an exchange between [14C]UDP and UDP-glucose was found. The bisubstrate kinetics of the enzyme for UDP-glucose and glycogen, as well as for UDP-glucose and maltose, was determined. An intersecting pattern in the double reciprocal plot (velocity versus substrate concentration) suggestive of a sequential mechanism (ordered or random) was found in all cases. The K-m for UDP-glucose (45 to 48 mM) was the same with either maltose or glycogen as acceptor. The K-m for maltose (230 mM) and for glycogen (1.5 mug/ml) differed.
Assuntos
Glicogênio Sintase/metabolismo , Músculos/enzimologia , Animais , Glicerol/farmacologia , Glicogênio , Glicogênio Sintase/isolamento & purificação , Cinética , Maltose , Cloreto de Potássio/farmacologia , Conformação Proteica , Coelhos , Uridina Difosfato Glucose/metabolismoRESUMO
Glycogen synthase purified to homogeneity from rabbit skeletal muscle is essentially free of carbohydrate and shows no activity in the absence of added acceptor. It can use glucose as a substrate converting it to a glucose disaccharide in the presence of UDP-glucose as cosubstrate. The reaction is dependent on time, and on UDP-glucose, glucose, and enzyme concentrations. The product of the single step reaction co-chromatographs in two solvent systems with maltose. The glucose disaccharide produced in the reaction with UDP-[14-C]glucose and nonradioactive glucose as well as with nonradioactive UDP-glucoes and [14-C]glucose is labeled asymmetrically. The linkage is characterized as alpha-1,4 and therefore the disaccharide is identified as maltose.
