Differentiation of the nucleotide pyrophosphatases of rat-liver plasma membranes and endoplasmic reticulum by enzymic iodination.

Enzymic iodination of isolated rat hepatocytes and of rat livers perfused in situ was used to discriminate between the nucleotide pyrophosphatases of endoplasmic reticulum and of plasma membranes. The location of the latter on the cell surface could also be substantiated by this method. The activity of the microsomal enzyme increased after phenobarbital treatment of the animals. The nucleotide pyrophosphates from both subcellular fractions were solubilized, purified to electrophoretic homogeneity, and their 125I content determined. The labelling of the enzyme obtained from plasma membranes was several-fold higher than that of the nucleotide pyrophosphatase from endoplasmic reticulum. This indicates a bimodal distribution of nucleotide pyrophosphatase in rat liver and the accessibility of the plasma membrane enzyme from the extracellular space.