Comparison of sarcoplasmic reticulum Ca²⁺-adenosine triphos-phatase from vitamin E-deficient dystrophic rabbit skeletal muscle with iron-ascorbate-treated and untreated enzyme

Abstract

Sarcoplasmic reticulum Ca 2+ ATPase from rabbit skeletal muscle has an Arrhenius curve of enzyme activity with a discontinuity at about 20°C. Preparations treated with FeSO 4 and ascorbic acid and from a vitamin E-deficient dystrophic rabbit have 22% of the normal activity and a linear Arrhenius curve (Promkhatkaew, D., Komaratat, P., & Wilairat, P. (1985) Biochem. Int. 10, 937-943). All three preparations were cross-linked to the same extent by dimethyl suberimidate and copper-phenanthroline reagent at temperatures above and below the temperature of the Arrhenius discontinuity. Both iron-ascorbate-treated Ca 2+ -ATPase and that from a vitamin E-deficient animal had 50% of the normal sulfhydryl content, but the disulfide and free amino contents were unaltered. These observations suggest that loss of sulfhydryl groups through lipid peroxidation, both in vivo and in vitro, resulted in reduction of Ca 2+ -ATPase activity and loss of the break in the Arrhenius plot. Changes in Ca 2+ -ATPase polypeptide aggregational state could not account for the discontinuity in the Arrhenius curve as revealed by the similar extent of cross-linking of the three enzyme preparations at temperatures above and below the temperature of the Arrhenius discontinuity. © 1988 BY THE JOURNAL OF BIOCHEMISTRY.