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.
Istituto di Biochimica, Facoltà di Medicina, Ancona, Italy.
G
G
Zolese
R
R
Staffolani
L
L
Mazzanti
E
E
Gratton
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