ATP‐dependent calcium transport in rat parotid microsomes. I. Localization, properties, Ca2+‐ATPase activity and phosphoenzyme formation

Abstract
ATP‐dependent Ca2+ transport was studied in rat parotid microsomes; the activity appears to be associated with rough endoplasmic reticulum vesicles, as indicated by marker distribution in subcellular fractions and by electron microscopic observations. Purified rough microsomes exhibit an ATP‐dependent Ca2+ accumulation and a Ca2+‐dependent ATPase activity; these activities are similarly stimulated by K+ and display an apparent Km for free calcium of 0.6‐0.7 microM. A phosphoprotein, with a molecular weight of about 110,000, was detected after short incubation with [gamma 32P] ATP and CaCl2; it is suggested that this compound represents a phosphorylated intermediate form of the Ca2+‐ATPase.

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