Different sensitivity of ATP + Mg + Na (I) and Pi + Mg (II) dependent types of ouabain binding to phospholipase A2.
The effect of phospholipase A2 and of related agents on ouabain binding and Na, K-ATPase activity were studied in intact and detergent-treated membrane preparations of rat brain cortex and pig kidney medulla. It was found that phospholipase A2 (PLA2) may distinguish or dissociate ouabain binding complexes I (ATP + Mg + Na) and II (Pi + Mg), stimulating the former and inhibiting the latter. Procedures which break the permeability barriers of vesicular membrane preparations, such as repeated freezing-thawing, sonication or hypoosmotic shock failed to mimic the effect of PLA2, indicating that it was not acting primarily by opening the inside-out oriented vesicles. The detergent digitonin exhibited similar effects on ouabain binding in both ATP + Mg + Na and Pi + Mg media. Other detergents were ineffective. The ability of PLA2 to distinguish between ouabain binding type I and II can be manifested even in SDS-treated, purified preparations of Na, K-ATPase. The number of ATP + Mg + Na-dependent sites is unchanged, while the Pi + Mg-dependent sites are decreased in number in a manner similar to that seen in original membranes. This inhibition is completely lost in the reconstituted Na, K-ATPase system, where the ATP- as well as Pi-oriented ouabain sites are inhibited by PLA2.
Svoboda
P
P
Institute of Physiology, Czechoslovak Academy of Sciences, Praha.
Amler
E
E
Teisinger
J
J
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D010042:Ouabain / Q000378:metabolism*; D010739:Phospholipase D / Q000494:pharmacology; D010740:Phospholipases / Q000494:pharmacology*; D010741:Phospholipases A / Q000494:pharmacology*; D054467:Phospholipases A2; D010758:Phosphorus / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D010738:Type C Phospholipases / Q000494:pharmacology
D010758:Phosphorus; D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases; D010739:Phospholipase D; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium