RESUMO
Genesine, the naked autoglucosylating protein involved in glycogen biosynthesis, was partially purified from rat liver and some of its biochemical properties were characterized. Its activity was strongly activated by Mn2+ and two-pH optimums were obtained. UDP-14C-Glc was the preferred glucosyl donor substrate, but also UDP-14C-Xyl was. It was additionally found that more than one glucose was transferred to the protein or to that alpha1,4 glucan already linked to the protein from UDP-Glc. Glucose, maltose, xylose and UDP were inhibitors of genesine activity.
Assuntos
Glicoproteínas/isolamento & purificação , Glicosiltransferases , Fígado/química , Animais , Metabolismo dos Carboidratos , Cátions , Glicoproteínas/química , Concentração de Íons de Hidrogênio , Proteoglicanas/biossíntese , Ratos , Temperatura , Fatores de Tempo , Uridina Difosfato Glucose/metabolismoRESUMO
Different branching enzymes were partially purified in order to get some insight into their mechanism of action. Each branching enzyme is able to synthesize in vitro at any moment, even during very short incubation times, only one type of alpha 1,4-alpha 1,6 glucopolysaccharide, which possesses unique and specific properties (lambda max; A; R;% of beta-amylolysis;% alpha 1,6). Between two branching points, each branching enzyme will leave, in average, a constant and specific number of glucoses alpha 1,4-linked, which is characteristic of that particular enzyme. Consequently the structure of the polysaccharide will keep the same independently from the moment of synthesis.
Assuntos
Enzima Ramificadora de 1,4-alfa-Glucana/metabolismo , Enzima Ramificadora de 1,4-alfa-Glucana/isolamento & purificação , Animais , Configuração de Carboidratos , Glucanos/biossíntese , Glucanos/química , Glucose/química , Glucose/metabolismo , Glicogênio/biossíntese , Glicogênio/química , Técnicas In Vitro , Fígado/enzimologia , Modelos Biológicos , Polissacarídeos/biossíntese , Polissacarídeos/química , Ratos , Solanum tuberosum/enzimologia , Espectrofotometria , Zea mays/enzimologiaRESUMO
Starch biogenesis in corn endosperm from Flint, Sugary, Waxy, as a function of the grain filling/period was studied. We have differentially identified the initiation from the elongation process. After incubating under unprimed conditions, two glucose radiolabelled protein bands of 39,5 and 36 kDa were obtained. UDP(14C)Glc was the preferred glucosyl donor but also ADP(14C)Glc was. It was additionally found that more than one glucose was transferred to the protein or to the alpha 1,4-glucan linked to protein from UDPGlc. These results were supported by the fact that the glucosylated protein from UDPGlc liberates maltooligosaccharides after alpha- or beta-amylase treatment. The elongation activity in the first steps related to the glucan linked to protein is different from starch synthase. Therefore, we are proposing a model for starch biogenesis where two new transglucosylating enzyme activities are necessary to prepare the primer for starch synthase.