Ascorbic acid-Fe2+ treatment mimics effect of vitamin E deficiency on sarcoplasmic Ca-ATPase of rabbit muscle

After 90 min treatment with ascorbic acid and FeSO4 at 4 degrees C, the activity of rabbit sarcoplasmic reticulum Ca-ATPase was reduced to 22% and the Arrhenius plot of enzyme activity showed an absence of a discontinuity. The presence of vitamin E restored enzyme activity (60%) and the discontinuity in the Arrhenius plot. Ca-ATPase reconstituted with delipidated protein from ascorbic acid-Fe-treated preparation and normal lipid exhibited properties similar to the intact treated enzyme, whereas that reconstituted with delipidated normal protein and lipid from treated preparation exhibited reduced activity but retained the Arrhenius discontinuity. These properties are similar to those observed for sarcoplasmic reticulum Ca-ATPase from the vitamin E-deficient muscular dystrophic rabbit.