Properties and Biosynthetic Connection of the Nucleotide Pyrophosphatases of Rat Liver Plasma Membrane and Endoplasmic Reticulum

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Abstract
The detergent-solubilized nucleotide pyrophosphatases of the rat liver plasma membrane and endoplasmic reticulum fractions were purified by lectin affinity chromatography. They have the same molecular mass of 148,000 dalton; their catalytic properties are also very similar and correspond to those of the trypsin-solubilized activities from the same membrane preparations. Pulse-chase experiments on isolated perfused livers using [3H]leucine indicated different labeling kinetics of the proteins isolated from plasma membrane and endoplasmic reticulum. The plasma membrane enzyme became only slightly labeled in the presence of 100 .mu.M vinblastine. The data support a precursor-product relationship of the nucleotide pyrophosphatases from endoplasmic reticulum and plasma membrane.