RESUMO
The characteristics of the basic amino acid permease (system VI) of the filamentous fungus Penicillium chrysogenum were studied in plasma membranes fused with liposomes containing the beef heart mitochondrial cytochrome c oxidase. In the presence of reduced cytochrome c, the hybrid membranes accumulated the basic amino acids arginine and lysine. Inhibition studies with analogs revealed a narrow substrate specificity. Within the external pH range of 5.5 to 7.5, the transmembrane electrical potential (delta psi) functions as the main driving force for uphill transport of arginine, although a low level of uptake was observed when only a transmembrane pH gradient was present. It is concluded that the basic amino acid permease is a H+ symporter. Quantitative analysis of the steady-state levels of arginine uptake in relation to the proton motive force suggests a H+-arginine symport stoichiometry of one to one. Efflux studies demonstrated that the basic amino acid permease functions in a reversible manner.
Assuntos
Arginina/metabolismo , Membrana Celular/metabolismo , Lisina/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Penicillium chrysogenum/metabolismo , Sistemas de Transporte de Aminoácidos , Sistema Livre de Células , Grupo dos Citocromos c/metabolismo , Concentração de Íons de Hidrogênio , Ionóforos/farmacologia , Cinética , Lipossomos/metabolismo , Potenciais da Membrana , Moduladores de Transporte de Membrana , Proteínas de Membrana Transportadoras/antagonistas & inibidores , Proteínas de Membrana Transportadoras/efeitos dos fármacos , Educação Física e TreinamentoRESUMO
Transport studies with Penicillium chrysogenum plasma membranes fused with cytochrome c oxidase liposomes demonstrate that sulfate uptake is driven by the transmembrane pH gradient and not by the transmembrane electrical potential. Ca2+ and other divalent cations are not required. It is concluded that the sulfate transport system catalyzes the symport of two protons with one sulfate anion.
Assuntos
Penicillium chrysogenum/metabolismo , Sulfatos/metabolismo , Transporte Biológico , Cálcio/metabolismo , Membrana Celular/metabolismo , Complexo IV da Cadeia de Transporte de Elétrons/metabolismo , Concentração de Íons de Hidrogênio , Lipossomos/metabolismo , Magnésio/metabolismoRESUMO
Functional plasma membranes from the filamentous fungus Penicillium chrysogenum have been isolated with the objective of studying transport processes. The isolation procedure consists of three steps, namely homogenization of cells with a Braun MSK homogenizer, followed by Percoll gradient centrifugation and floatation of membranes in a three-step Nycodenz gradient. This method can be applied to strains which differ significantly in morphology and penicillin-production capacity. Plasma membranes were fused with liposomes containing the beef heart mitochondrial cytochrome-c oxidase. In the presence of reduced cytochrome c, the hybrid membranes maintained a high proton motive force that functions as a driving force for the uptake of the amino acids arginine and valine via distinct transport systems.