Paraquat-stimulated binding of dopa to liver and lung microsomal protein.

1. 3H-Dopa is converted by lung and liver microsomes to a reactive intermediate which binds covalently to lung and liver microsomal protein. 2. Binding of radioactivity from 3H-dopa to lung and liver microsomes was decreased by superoxide dismutase to the level observed with boiled microsomes. 3. Paraquat (5 mM) caused a 133% increase in binding of radioactivity from 3H-dopa with lung microsomes compared with 224% increase with liver microsomes. However, superoxide dismutase decreased the binding by 38% and 50% with lung and liver microsomes respectively. 4. Benzoate and 1,4-diazobicyclo[2,2,2]octane in the absence and presence of paraquat had no effect on the binding of radioactivity from 3H-dopa. 5. Glutathione and ascorbic acid in the absence and presence of paraquat decreased the binding to below the level obtained with boiled microsomes. 6. The soluble fraction when present in the physiological ratio to microsomal protein decreased the binding, in the presence of paraquat, to the level of the control.