Effect of divalent cations on Na+,K(+)-ATPase obtained from human placenta.
Circular dichroism (CD) and acrylamide quenching studies of Na+,K(+)-ATPase from human placenta showed that its incorporation into phosphatidylcholine vesicles increased the enzymic activity by 55%. Moreover, both with the purified and the vesicle-reconstituted protein, Ca2+ and Mg2+ increased the activity, the effect being more pronounced after preincubation of the protein with Mg2+. CD data suggest that this activity increase may be linked to a change in the secondary structure of the ATPase, in particular beta-turn, beta-sheet and random coil. Acrylamide quenching studies suggest that ions could primarily interact with phospholipid head groups, but not directly with the protein.
Zolese
G
G
Istituto di Biochimica, Facoltà di Medicina, Ancona, Italy.
Staffolani
R
R
Mazzanti
L
L
Gratton
E
E
D002118:Calcium / Q000502:physiology*; D006801:Humans; D008274:Magnesium / Q000502:physiology*; D010920:Placenta / Q000201:enzymology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000378:metabolism*
D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D002118:Calcium