THE CATALYSIS OF ASCORBIC ACID OXIDATION BY COPPER AND ITS COMPLEXES WITH AMINO ACIDS, PEPTIDES, AND PROTEINS

Abstract

The oxidation of solutions of ascorbic acid catalyzed by copper and the copper complexes of amino acids, peptides, and proteins has been investigated by manometric and chemical means. The copper-containing solutions were prepared by equilibration with the sparingly soluble salt malachite. The catalytic activity of the complexed copper was found to be dependent upon the type of complexing molecule. For amino acids the more firmly bound copper atoms tended to be the best catalysts. The catalytic activity of the copper complexed to several glycine peptides was approximately one half of the mean value of that of the copper complexed to amino acids. The catalytic activity of copper complexed to bovine plasma albumen and pepsin was lower than that of copper complexed with amino acids or peptides. The more firmly bound copper atoms on pepsin showed a higher catalytic activity than the mean value for all the complexed copper atoms. Sodium chloride markedly reduced the catalytic activity of both free copper and complexed copper. In the absence of sodium chloride free copper was 10 times as effective a catalyst as copper complexed to glycine. In the presence of 0.178 M sodium chloride the complexed copper was twice as effective as free copper.