RESUMO
The tryptophan phosphorescence from a series of derivatives of Pseudomonas aeruginosa azurin has been monitored at 30 degrees C in pH 8.5 buffer solution. The phosphorescence lifetimes fall in the range of 230-270 ms for deoxygenated solutions of derivatives containing Cd(II), Cu(I), Co(II), Ni(II), Hg(II) or apoazurin. A weak signal with a lifetime of ca 130 ms is observed from solutions of oxidized native azurin, but this component is ascribed to a modified form of azurin in solution, i.e. protein heterogeneity, on the basis of the unique sensitivity to quenching by dioxygen. Aside from this minor component, the tryptophan phosphorescence in the Cu(II) protein appears to be fully quenched. The quenching is assigned an electron-transfer mechanism involving transient reduction of the metal center. The same mechanism is deemed to be responsible for fluorescence quenching in oxidized native azurin as well. These observations are of interest because aromatic groups like tryptophan may be conduits for physiological electron-transfer processes involving the copper center.
Assuntos
Azurina/efeitos da radiação , Azurina/análogos & derivados , Azurina/química , Transporte de Elétrons , Luminescência , Oxirredução , Fotoquímica , Temperatura , Triptofano/química , Triptofano/efeitos da radiaçãoRESUMO
Human serum proteins are found in significant density in the neuropil in brains of demented individuals. The functional significance of these abnormally distributed proteins has been unknown. We now report that alpha-globulin-enriched fractions of human serum decrease the specific binding of [3H]spiroperidol at its binding sites in postmortem human frontal cortex and caudate. The substances in this serum fraction apparently exert their effect by a direct action on the binding site. Since [3H]spiroperidol labels serotoninergic and dopaminergic among other neurotransmitter receptors, these results suggest that components of human serum inhibit the binding of ligands at neurotransmitter receptors.
