Immunoquantitation of rat erythrocyte superoxide dismutase: its use in copper deficiency

Two immunoassays have been developed for the determination of rat erythrocyte dismutase (Cu,Zn-SOD). An enzyme-linked immunosorbent assay (ELISA) was very sensitive down to 4 ng/ml with a coefficient of variation (CV) of 18% while the single radial immunodiffusion assay (SRID) permitted an adequate detection level (5 micrograms/ml) with far better accuracy (CV = 4.2%). The latter was thus selected for the determination of Cu,Zn-SOD in the red blood cells of normal and copper-depleted rats. The average value of Cu,Zn-SOD in normal adult rat erythrocytes was 1142 +/- 120 ng/mg hemoglobin. When compared to activity measurements, good correlation was obtained between enzyme content and enzyme activity (r = 0.803, P less than .001). In an experimental copper deficiency followed by supplementation, good correlation was observed in the course of depletion (r = 0.848, P less than .001) and repletion (r = 0.896, P less than .001). During depletion, the loss of enzyme activity was mainly related to a loss of enzyme. However, enzymatically inactive protein was formed which would be activated when copper was added. These results indicate the importance of a combined use of Cu,Zn-SOD immunoquantitation and activity measurements to enable a better understanding of changes occurring with respect to enzyme activity.