Isolation and characterization of skeletal acid ATPase--a new osteoclast marker?

A tartrate-resistant, iron-activated and vanadate-sensitive nucleotide tri- and diphosphatase has been purified from rat bone. The purified enzyme (1,400-fold, 45% yield) has an Mr on SDS-PAGE of 30,000 Da. Hydrodynamic properties include a Stokes radius of 24A, a sedimentation coefficient of 3.2 S and a partial specific volume of 0.748 ml/g. The calculated Mr from hydrodynamic data is 32,000 and the enzyme binds 4 mol Triton X-100/mol enzyme. Substrate specificity studies demonstrate that the enzyme is active against nucleotide tri- and diphosphates and phosphotyrosine, but not against phosphoserine or phosphothreonine. Based on the purification profile and enzyme histochemistry, showing labelling of fewer mononuclear cells using ATP compared to conventional acid phosphatase substrates, it is suggested that the acid ATPase constitutes a unique form in the family of tartrate-resistant acid phosphatases and may thus have the potential as a marker for osteoclast ontogeny and function.