Cardiac sarcoplasmic reticulum Ca2+ pump as a target for benzoquinones☆

Abstract 1. 1. Three benzoquinones ( p -benzoquinone, 2,5-dimethyl- p -benzoquinone) and tetramethyl-1,4-benzoquinone), differing for their electrophilicity, were tested on Ca 2+ ATPase activity of cardiac sarcoplasmic reticulum membrane vesicles. 2. 2. Only p -benzoquinone and 2,5-dimethyl- p -benzoquinone) inhibited Ca 2+ ATPase activity in a time-and concentration-dependent way, tetramethyl-1,4-benzoquinone being ineffective. 3. 3. p - Benzoquinone and 2,5-dimethyl- p -benzoquinone) decreased in a concentration-dependent way the total—SH groups of cardiac sarcoplasmic reticulum vesicles. 4. 4. The results suggest that the most electrophilic benzoquinones interact directly with some critical —SH groups of Ca 2+ pump inhibiting the enzymatic activity.