Characterization of an insoluble adenosine deaminase complexing protein from human kidney

Evidence for the presence of an insoluble form of adenosine deaminase complexing protein in human kidney has been obtained. An initial study demonstrated that binding of monomeric adenosine deaminase to particulate material from kidney was saturable and could be blocked by preincubating the enzyme with soluble complexing protein. Treatment of particulate material with deoxycholate, followed by immunoassay of the detergent extract, confirmed the presence of an insoluble form of complexing protein in the kidney. Several other human organs examined by this technique contained smaller amounts of insoluble complexing protein. Complexing protein isolated from the soluble and particulate fractions of kidney homogenates were found to be structurally similar. The proteins had the same subunit M_r and showed complete crossreactivity with antiserum to soluble complexing protein. Indirect immunoperoxidase staining of renal cortical tissue revealed that complexing protein was concentrated in the brush border of the proximal tubules. These results indicate that (a) the soluble and insoluble forms of complexing protein from human kidney may be products of the same gene(s) and (b) a portion of the complexing protein in human kidney is bound to the brush border membranes of cells lining the proximal tubules.