RESUMO
Hemoglobin (Hb) is a promiscuous protein that not only transports oxygen, but also catalyzes several biotransformations. A novel in vitro catalytic activity of Hb is described. Bovine Hb and human erythrocytes were found to display ATRPase activity, i.e., they catalyzed the polymerization of vinyl monomers under conditions typical for atom transfer radical polymerization (ATRP). N-isopropylacrylamide (NIPAAm), poly(ethylene glycol) methyl ether acrylate (PEGA), and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were polymerized using organobromine initiators and the reducing agent ascorbic acid in acidic aqueous solution. In order to avoid chain transfer from polymer radicals to Hb's cysteine residues, the accessible cysteines were blocked by a reaction with a maleimide. The formation of polymers with bromine chain ends, relatively low polydispersity indices (PDI), first order kinetics and an increase in the molecular weight of poly(PEGA) and poly(PEGMA) upon conversion indicate that control of the polymerization by Hb occurred via reversible atom transfer between the protein and the growing polymer chain. For poly(PEGA) and poly(PEGMA), the reactions proceeded with a good to moderate degree of control. Sodium dodecyl sulfate (SDS) gel electrophoresis, circular dichroism spectroscopy, and time-resolved ultraviolet-visible (UV-vis) spectroscopy revealed that the protein was stable during polymerization, and only underwent minor conformational changes. As Hb and erythrocytes are readily available, environmentally friendly, and nontoxic, their ATRPase activity is a useful tool for synthetic polymer chemistry. Moreover, this novel activity enhances the understanding of Hb's redox chemistry in the presence of organobromine compounds.
Assuntos
Ácido Ascórbico/química , Eritrócitos/química , Radicais Livres/química , Hemoglobinas/química , Resinas Acrílicas/química , Animais , Biocatálise , Bovinos , Humanos , Concentração de Íons de Hidrogênio , Cinética , Oxirredução , Polietilenoglicóis/química , Polimerização , Ácidos Polimetacrílicos/química , Polivinil/química , Estabilidade Proteica , Substâncias Redutoras/químicaAssuntos
Biocatálise , Peroxidase do Rábano Silvestre/metabolismo , Acrilamidas/química , Acrilamidas/metabolismo , Resinas Acrílicas , Radicais Livres/química , Radicais Livres/metabolismo , Peroxidase do Rábano Silvestre/química , Modelos Moleculares , Estrutura Molecular , Polimerização , Polímeros/química , Polímeros/metabolismoRESUMO
The hemoprotein horseradish peroxidase (HRP) catalyzes the polymerization of N-isopropylacrylamide with an alkyl bromide initiator under conditions of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) in the absence of any peroxide. This is a novel activity of HRP, which we propose to name ATRPase activity. Bromine-terminated polymers with polydispersity indices (PDIs) as low as 1.44 are obtained. The polymerization follows first order kinetics, but the evolution of molecular weight and the PDI upon increasing conversion deviate from the results expected for an ATRP mechanism. Conversion, M(n) and PDI depend on the pH and on the concentration of the reducing agent, sodium ascorbate. HRP is stable during the polymerization and does not unfold or form conjugates.
