Purification of an adenosine deaminase complexing protein from human plasma

A protein which specifically complexes with adenosine deaminase (complexing protein) has been purified to homogeneity from human plasma. This protein was compared with complexing protein isolated from human kidney. The two proteins produce electrophoretically different forms of high molecular weight adenosine deaminase when combined with the Mr = 36,000 enzyme monomer from erythrocytes. This difference may, at least in part, be due to the greater sialic acid content of complexing protein from plasma. By other criteria, including amino acid composition, total carbohydrate content, and subunit structure, the two proteins are quite similar. In addition, plasma complexing protein shows complete cross-reactivity with anti-kidney complexing protein serum. These results suggest that plasma and kidney complexing proteins are products of the same gene.