On the Form of Copper in Blood Plasma*

Although copper has been the subject of numerous researches which have demonstrated that it is essential for normal hemoglobin formation, there have been very few attempts to discover the type of compound in which the element occurs in the case of red blooded animals. Warburg and Krebs (1) approached the problem in experiments on what was referred to as loosely bound copper in blood serum. Using the Warburg apparatus, they found that blood serum plus 1 volume of 0.2 N HCl would catalyze the oxidation of cysteine just as effectively as the ash of the serum. These workers calculated the copper content of the serum on the basis of its catalytic activity. Tompsett (2) reported that trichloroacetic acid filtrates contained all of the copper of the original blood. Eisler, Rosdahl, and Theorell (3) found the rates of migration of copper ions to be the same as that of serum albumin molecules in cataphoresis experiments with horse serum. From this they concluded that the copper and the albumin were combined into a complex. They supported their contention with the observation that when the protein was precipitated below its isoelectric point the copper went into the filtrate, and when the protein was precipitated above the isoelectric point, the filtrate was free from copper. There have been a number of studies on “loosely bound” or “easily split off” iron in blood, chiefly by Barkan and coworkers. Moore et aZ. (4, 5) have recently published an extensive investiga-