Biology of tartrate-resistant acid phosphatase

Tartrate-resistant acid phosphatase (TRAP) is a member of the ubiquitously expressed enzyme family of the acid phosphatases. Nearly 30 years ago, TRAP became known to hematologists as cytochemical marker enzyme of hairy cell leukemia. Physiologically, TRAP is primarily a cytochemical marker of macrophages, osteoclasts and dendritic cells. TRAP is localized intracellularly in the lysosomal compartment. Recent data suggest also secretion of TRAP by some cell types, in particular by osteoclasts. Human, mouse and rat TRAP are biochemically well characterized. While the complete genomic sequence of TRAP has been elucidated, only limited information on the genetic details of the gene and its regulation is available. It appears that the intracellular iron content is involved in the regulation of the enzyme. The physiological substrates for this enzyme have not been identified yet and consequently the functional role of TRAP remains completely unknown, though some hypotheses have been forwarded, e.g. involvement in bone resorption and iron homeostasis (transport, metabolism). Taken together, research on the biology of TRAP has been intensive and has led to considerable progress on a number of fronts, including the cloning of the gene. Further studies are, however, still required to determine the role of TRAP in vivo.