Copper metabolism in the plaice, Pleuronectes platessa (L.) : purification and characterization of ceruloplasmin, a copper-dependent enzyme
The work described in this Thesis was conducted to investigate aspects of copper metabolism in the plaice Pleuronectes platessa (L). Three major aspects were studied. The first was to investigate and partially characterize the distribution of copper and copper-dependent enzymes in the various tissues of the plaice. The second was to study the effect of cadmium on copper-dependent enzymes as a base line for understanding the competition between an essential metal ion and a non-essential toxic metal ion. This has established a foundation for the interpretation of the toxicity of pollutants to a marine organism. The third and the major part of the investigation was to purify and characterize the copper-dependent enzyme, ceruloplasmin, and to compare it with the isolated enzyme from the mammalian system. The results from the first part of the investigation showed that (i) Copper is relatively evenly distributed in the plaice. Apart from brain which has the highest concentration of copper, the concentrations of copper in the other tissues generally reflect the copper-dependent enzyme activities. (ii) The presence of the copper-dependent enzymes in the plaice are confirmed. The assay system used for the mammalian enzyme systems apply reasonably well to the plaice enzymes. (iii) The limited study on the relatively crude preparations of copper-dependent enzymes show that they are similarly distributed in mammals and that they have similar properties. Cytochrome oxidase, however, has a higher pH optimum than that of the mammalian enzymes. Exposure of the plaice to sublethal concentrations of cadmium as cadmium chloride results in initial increase in ceruloplasmin, cytochrome oxidase, monomaine oxidase and tryptophan oxygenase activities followed by a decrease after a prolonged exposure. Changes in the copper-dependent enzyme activities are accompanied by parallel changes in the concentrations of copper in the serum and liver. Thus cadmium alters copper metabolism in the plaice.