Postnatal decline of (Ca2+ + Mg2+)-activated membrane ATPase in cattle red cells.

Acitivity of membrane bound (Ca2+ + Mg2+)-stimulated ATPase, associated with Ca2+ outward transport, in calf red cells is high at birth and declines with a rate constant of 0.041 d-1 after the 3rd week. The decline parallels the disappearance of fetal hemoglobin.