RESUMO
UNLABELLED: Mutations that cause the constitutive expression of the PHO regulon of Escherichia coli occur either in the pst operon or in the phoR gene, which encode, respectively, a high-affinity Pi transport system and a histidine kinase sensor protein. These mutations are normally selected on glycerol-2-phosphate (G2P) as the carbon source in the presence of excess Pi. The emergence of early PHO-constitutive mutants, which appear after growth for up to 48 h on selective medium, depends on the presence of phoA, which codes for a periplasmic alkaline phosphatase, while late mutants, which appear after 48 h, depend both on phoA and on the ugp operon, which encodes a glycerophosphodiester transport system. The emergence of the late mutants hints at an adaptive mutation process. PHO-constitutive phoR mutants appear only in a host that is mutated in pitA, which encodes an alternative Pi transport system that does not belong to the PHO regulon. The conserved Thr(217) residue in the PhoR protein is essential for PHO repression. IMPORTANCE: One of the principal ways in which bacteria adapt to new nutrient sources is by acquiring mutations in key regulatory genes. The inability of E. coli to grow on G2P as a carbon source is used to select mutations that derepress the PHO regulon, a system of genes involved in the uptake of phosphorus-containing molecules. Mutations in the pst operon or in phoR result in the constitutive expression of the entire PHO regulon, including alkaline phosphatase, which hydrolyzes G2P. Here we demonstrate that the ugp operon, another member of the PHO regulon, is important for the selection of PHO-constitutive mutants under prolonged nutritional stress and that phoR mutations can be selected only in bacteria lacking pitA, which encodes a secondary Pi transport system.
Assuntos
Proteínas de Escherichia coli/metabolismo , Escherichia coli/metabolismo , Proteínas de Transporte de Fosfato/metabolismo , Regulon/fisiologia , Escherichia coli/genética , Proteínas de Escherichia coli/genética , Deleção de Genes , Regulação Bacteriana da Expressão Gênica , Família Multigênica , Óperon , Proteínas de Transporte de Fosfato/genética , Seleção Genética , Fatores de TempoRESUMO
Os inibidores da enzima acetilcolinesterase (AChE) são uma das principais classes de medicamentos utilizadas no tratamento de sintomas de doenças neurodegenerativas como a doença de Alzheimer (DA), pois são capazes de elevar os níveis de acetilcolina no cérebro. Plantas têm sido uma excelente alternativa na busca de novas moléculas bioativas. No presente trabalho, extratos alcoólicos dos frutos de Myrcianthes pungens (O.Berg) D.Legrand (Myrtaceae), também conhecidos como guabijú ou guabiroba-açú, foram investigados quanto à capacidade de inibição de AChE in vitro por ensaio bioautográfico, utilizando o reagente Fast Blue Salt B. Foi observada a presença de pelo menos quatro diferentes substâncias com capacidade inibitória de AChE nos frutos verdes e maduros desta espécie. Duas das substâncias ativas foram caracterizadas como terpenos por meio de ensaios com reagentes específicos em cromatografia de camada delgada. Estes resultados correspondem ao primeiro relato da atividade de inibição de AChE em espécies do gênero Myrcianthes (Myrtaceae).
Inhibitors of the acetylcholinesterase enzyme (AChE) are one of the major classes of drugs used in the treatment of symptoms of neurodegenerative diseases like Alzheimer?s disease (AD), because they can increase the levels of acetylcholine in the brain. Plants have been an excellent alternative source of bioactive molecules. In the present study, alcoholic extracts of fruits of Myrcianthes pungens (O.Berg) D.Legrand (Myrtaceae), also known as ?guabijú? or ?guabiroba-açú?, were investigated for their ability to inhibit AChE in vitro in a bioautographic assay using Fast Blue Salt B reagent. The presence of at least four different substances capable of inhibiting AChE in unripe and ripe fruits of this species was observed. Two active substances were characterized as terpenes in assays using specific reagents with thin layer chromatography. These results are the first report of the AchE inhibition activity for species of Myrcianthes genus (Myrtaceae).