Polysaccharides as enzymes? The oxidation of catecholamines by Cu(II) or Fe(II) in the presence of chondroitin sulfate A or C.

摘要

The Cu(II) or Fe(II)-mediated oxidation of the catecholamines dopamine, epinephrine and norepinephrine was studied in the presence of various polysaccharides. Although many types of polysaccharides were tested, this research focused on the effects of chondroitin sulfate type A and C as these polysaccharides are present in the extracellular matrix of nerve cells and could interact with catecholamine-based neurotransmitter in vivo. The oxidation of the catecholamines was significantly enhanced in the presence of both types of chondroitin sulfate as evidenced from kinetic experiments using UV_Vis spectroscopy. Size exclusion chromatography revealed that the oxidation products may be bound to the chondroitin sulfate polysaccharides indicating a physic-chemical interaction between both. The effect of cation, polysaccharide and catecholamine concentration on the kinetics of the oxidation reactions were studied. Some data modeled with the Michaelis-Menten equation as if the polysaccharide and cation combination acted as an enzyme. Specifically, our observations indicate that the chondroitin sulfate polysaccharides could have a direct, biochemical affect on the function of neurotransmitters. But in a more general perspective, a hypothesis is raised and discussed that polysaccharides could have enzyme-like properties and constitute, together with ribozymes, an innate branch of enzymology in contrast to the protein-based enzymes; referred to as the adaptive branch of enzymology.