title: Stimulatory and inhibitory effects of dimethylsulfoxide, propranolol and chlorpromazine on the partial reactions of ATPase of sarcoplasmic reticulum.
abstract: The effects of dimethylsulfoxide, propranolol and chlorpromazine on the partial reactions of the ATPase of sarcoplasmic reticulum were investigated. When analyzed according to a reaction scheme in which the ADP-sensitive (E1P) and ADP-insensitive (E2P) phosphoenzymes occur sequentially and P1 is derived from the latter, dimethylsulfoxide decreased the rate of E2P hydrolysis whereas it stimulated the rate of the E1P to E2P conversion. Propranolol increased the rate of E2P hydrolysis while it decreased the rate of the E1P to E2P conversion. Propranolol exerted an additional effect, presumably inhibition of the phosphoenzyme formation. These effects of dimethylsulfoxide and propranolol can account for both the stimulatory and inhibitory effects of these drugs on the overall rate of ATP hydrolysis observed in the presence and absence of added alkali metal salts. Chlorpromazine accelerated E2P hydrolysis whereas it appeared to inhibit the E1P to E2P conversion. These effects of chlorpromazine appear able to account for its stimulatory and inhibitory effects on the overall rate of ATP hydrolysis in the presence and absence of alkali metal salts. In the presence of chlorpromazine, however, the rate of Pi liberation during the steady state ATP hydrolysis was found to be greater than the hydrolysis rate of E2P. This finding suggests that under these conditions Pi is derived not only from E2P but also from source(s) other than E2P.
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002746:Chlorpromazine / Q000494:pharmacology*; D004121:Dimethyl Sulfoxide / Q000494:pharmacology*; D004789:Enzyme Activation; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000201:enzymology; D011189:Potassium Chloride / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D000244:Adenosine Diphosphate; D011189:Potassium Chloride; D011433:Propranolol; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002746:Chlorpromazine; D004121:Dimethyl Sulfoxide