Activity and expression of banana starch phosphorylases during fruit development and ripening

Abstract

Two main forms of starch phosphorylase (EC 2.4.1.1) were identified and purified from banana (Musa acuminata Colla. cv. Nanicão) fruit. One of them, designated phosphorylase I, had a native molecular weight of 155 kDa and subunit of 90 kDa, a high affinity towards branched glucans and an isoelectric point around 5.0. The other, phosphorylase II, eluted at a higher salt concentration from the anion exchanger, had a low affinity towards branched glucans, a native molecular weight of 290 kDa and subunit of 112 kDa. Kinetic studies showed that both forms had typical hyperbolic curves for orthophosphate (Pi) and glucose-1-phosphate, and that they could not react with substrates with a blocked reducing end or alpha-1,6 glucosidic bonds. Antibodies prepared against the purified type-II form and cross-reacting with the type-I form showed that there was an increase in protein content during development and ripening of the fruit. The changes in protein level were parallel to those of phosphorylase activity, in both the phosphorolytic and synthetic directions. Considering the kinetics, indicating that starch phosphorylases are not under allosteric control, it can be argued that protein synthesis makes a contribution to regulating phosphorylase activity in banana fruit and that hormones, like gibberellic acid and indole-3-acetic acid, may play a regulating role. For the first time, starch phosphorylases isoforms were detected as starch-granule-associated proteins by immunostaining of SDS-PAGE gels.

Mutation of the Plastidial α-Glucan Phosphorylase Gene in Rice Affects the Synthesis and Structure of Starch in the Endosperm

“…Two types of starch phosphorylase (Pho) were observed in the following organs of higher plants: spinach (Spinacia oleracea) leaves (Steup and Schä chtele, 1981), pea (Pisum sativum) cotyledons (van Berkel et al, 1991), potato (Solanum tuberosum) leaves (St-Pierre and Brisson, 1995), fava bean (Vicia faba) cotyledons (Buchner et al, 1996), banana (Musa acuminata) fruits (da Mota et al, 2002), and wheat (Triticum aestivum) endosperm (Schupp and Ziegler, 2004). The two Pho types differ from each other not only in structure and kinetic properties but also in their expression pattern and subcellular localization (Steup, 1990).…”

Influência do ácido giberélico na degradação do amido durante o amadurecimento da banana

“…As enzimas desramificadoras, que atuam nas ligações α-1,6, podem liberar maltotriose, maltose e outros oligossacarídeos, fornecendo substratos para a atuação de outras enzimas, até açúcares solúveis, com geração de energia para a manutenção do fruto. Durante o amadurecimento da banana, as α e β-amilases [1,22], as fosforilases [18] e as α-1,4 e α-1,6-glicosidases [3,11] têm aumento de atividade, concomitante com a degradação do amido. Apesar de existirem evidências de que as amilases iniciam a degradação do amido da banana [12], as fosforilases não podem ser ainda descartadas, porque praticamente não existem trabalhos focalizando o assunto.…”

Influência da aplicação de ácido indol-3-acético na expressão dos receptores de etileno e na atividade de duas enzimas relacionadas ao metabolismo de amido em bananas

“…Como bem documentado, o metabolismo de amido é reconhecidamente coordenado por etileno MAINARDI et al, 2006;MOTA et al, 2002 (YAU et al, 2004) e AIA em raiz de alface promove incremento nos níveis de ERS1 (TAKAHASHI et al, 2010).…”