Evidence that tartrate-resistant acid phosphatases from osteoclastomas and hairy cell leukemia spleen are members of a multigene family.

1. Osteoclasts and hairy cell leukemia spleen both contain large amounts of a band 5-tartrate-resistant acid phosphatase (TrACP). 2. We have recently purified to homogeneity a band 5 TrACP from human osteoclastomas and two isoforms of band 5 TrACP (5a and 5b) from the spleen of a patient with hairy cell leukemia. 3. Although the N-terminal amino acid sequences and the apparent molecular weights of the osteoclastoma, hairy cell leukemia spleen TrACPs were identical, there were several differences in the physical and biochemical properties between the three isoenzymes. 4. Based on these findings, it is concluded that these isoenzymes are different enzymes, but that they could have originated from a similar ancestral gene. 5. It is proposed that the osteoclastoma and hairy cell leukemia band 5 TrACPs are members of a multigene family.