CARDIAC SARCOPLASMIC-RETICULUM CA2+ PUMP AS A TARGET FOR BENZOQUINONES

1. Three benzoquinones (p-benzoquinone, 2,5-dimethyl-p-benzoquinone an d tetramethyl-1,4-benzoquinone), differing for their electrophilicity, were tested on Ca(2+)ATPase activity of cardiac sarcoplasmic reticulu m membrane vesicles. 2. Only p-benzoquinone and 2,5-dimethyl-p-benzoqu inone inhibited Ca(2+)ATPase activity in a time- and concentration-dep endent way, tetramethyl-1,4-benzoquinone being ineffective. 3. p-Benzo quinone and 2,5-dimethyl-p-benzoquinone decreased in a concentration d ependent way the total SH groups of cardiac sarcoplasmic reticulum ves icles.4. The results suggest that the most electrophilic benzoquinones interact directly with some critical SH groups of Ca2+ pump inhibitin g the enzymatic activity.