Characterization of human adenosine deaminase

A deficiency of adenosine deaminase in man is associated with one form of severe combined immunodeficiency disease. In an attempt to define the nature of this relationship we have characterized the normal human enzyme and examined the role of this enzyme in monocyte-macrophage activation. The human enzyme was purified 800 000-fold to apparent homogeneity from human erythrocytes with 31% recovery by immunoabsorbent chromatography. The homogeneous protein contains carbohydrate and has a subunit molecular weight of 42 000, estimated by sodium dodecyl sulphate gel electrophoresis. The enzyme was found to exist in either a soluble or a particulate form. The active soluble forms are interconvertible with apparent molecular weights of 36 000 (small), 114 000 (intermediate), and 298 000 (large). However, conversion of the small form into the large form needs a protein with a molecular weight of 200 000 which has no adenosine deaminase activity.