Changes in enzyme expression related to differentiation and regulatory factors: the acid phosphatase of osteoclasts and other macrophages.

Human tartrate-resistant Type 5 acid phosphatase is a unique isoenzyme encoded by a gene located on chromosome 19. It is a member of a widely-distributed and structurally highly-conserved group of iron-containing proteins. It is normally expressed in certain tissue macrophages, notably osteoclasts and alveolar macrophages, but is virtually absent from the precursor monocytes. Factors which enhance or inhibit expression of this specific isoenzyme can be studied in monocytes and osteoclasts cultured in vitro. This provides opportunities to develop the use of Type 5 acid phosphatase as a reporter of pathophysiological events and an essential, though not sufficient, role in bone resorption by osteoclasts has been established by such studies.