The adenosine deaminase binding protein of human skin fibroblasts is located on the cell surface

We have studied the cellular localization of human adenosine deaminase binding protein in human skin fibroblasts. The binding activity sediments with the membrane fractions in a subcellular fractionation, and anti-binding protein antiserum reacts with the cell surface of intact fibroblasts, as shown by indirect immunofluorescence. The surface of intact fibroblasts binds 125I-labeled adenosine deaminase with an apparent KD of 0.26 units/ml and a maximum binding capacity of 553 milliunits/mg of cell protein. This binding is inhibited by antibinding protein antiserum. We conclude that most, if not all, of the adenosine deaminase binding protein is located on the cell surface.