[Molecular weight and subunit composition of GABA(A)-ergic compound-sensitive Cl-, HCO3(-)-stimulated Mg2+ ATPase from the plasma membrane of carp brain (Cyprinus carpio L.)].

Molecular weight and subunit composition of Cl-, HCO3(-), and picrotoxin-stimulated Mg(2+)-ATPase solubilized with sodium deoxycholate from the plasma membrane fraction of fish brain were studied by gel filtration. These enzymes were eluted from a Sephacryl S-300 column as a single peak and corresponded to a -300 kDa protein with a Stokes radius of 5.4 nm. The enzyme-enriched fraction concentrated and denatured by SDS was eluted from a Sephacryl S-200 column as a single subunit with a molecular weight of -56 kDa. SDS-PAGE also revealed a single major protein band with a molecular weight of -56 kDa. It was concluded that the molecular weight and subunit composition of CCl-, HCO3(-)-stimulated Mg(2+)-ATPase isolated from the plasma membrane of fish brain are similar to those of GABAA/benzodiazepine receptor complex from fish brain but differ from those of P-type transport ATPases.