Interaction between Ascorbic Acid and Cu-Proteins: Atomic Absorption and ESR Measurements on Erythrocyte Ghosts and Blood Plasma

Abstract

Lyophilized samples of mixtures of healthy native blood or erythrocytes with ascorbic acid exhibit an electron spin resonance (ESR) signal which has been obtained with leukemic blood. In order to find out whether membrane constituents are involved in the ascorbic acid interaction, white ghosts of erythrocytes were prepared according to the method of Dodge et al. (Arch. Biochem. Biophys. 100 (1963) 119). Lyophilized white ghosts which contained ≤ 0.1% of the erythrocyte hemoglobin didn’t show any ESR signal. Addition of ascorbic acid resulted in the typical “leukemic” ESR signal. Since similar changes were also observed in the plasma the receptor of vitamin C has to be searched for, therefore, in the membrane and plasma as well. It should be pointed out that the additional peak caused be the interaction with vitamin C is already present in plasma of healthy persons. In the case of leukemic patients the spin concentration is, however, reduced considerably. Based on previous findings, metallo proteins might function as receptors for vitamin C. Samples of ascorbic acid and catalase or cytochrome c didn’t reveal the ESR spectrum of leukemic blood. Copper containing proteins (e.g. ceruloplasmin, cytochrom-c-oxidase, haemocyanin), however, exhibit the “leukemic” signal when mixed with ascorbic acid. From this, it might be concluded that copper must be present in the membrane. Atomic absorption studies have shown that Cu is present in white ghosts (4×104 Cu atoms/WG). Furthermore, the copper content of leukemic plasma is about twice of that of healthy one, while the Fe content is diminished. Thus, the signal observed in leukemic blood seems to be due to a copperprotein-ascorbic acid interaction. In the case of leukemia, the vitamin C metabolism seems to be modified.