title: Tartrate-resistant acid phosphatase 5B circulates in human serum in complex with alpha2-macroglobulin and calcium.
abstract: Tartrate-resistant acid phosphatase (TRACP) is an enzyme with unknown biological function. In addition to its acid phosphatase activity, TRACP is capable of generating reactive oxygen species (ROS) at neutral pH. Two forms of TRACP circulate in human serum, macrophage-derived TRACP 5a and osteoclast-derived TRACP 5b. Here we have studied the circulating forms of the osteoclast-derived TRACP 5b in rat and human serum. In human serum, TRACP 5b circulates in a large complex that contained alpha2M and calcium. On the contrary, rat serum TRACP 5b circulates as a free molecule. Formation of the TRACP 5b complex in vitro decreased significantly the ROS generating activity of TRACP 5b without affecting its phosphatase activity. These results suggest that the complex formation may be necessary to eliminate the formation of the harmful ROS in the neutral pH of serum.
authors.affiliation: Department of Anatomy, Institute of Biomedicine, University of Turku, 20520 Turku, Finland.
authors.forename: Hannele
authors.initials: H
authors.lastname: Ylipahkala
authors.forename: Jussi M
authors.initials: JM
authors.lastname: Halleen
authors.forename: Helena
authors.initials: H
authors.lastname: Kaija
authors.forename: Pirkko
authors.initials: P
authors.lastname: Vihko
authors.forename: H Kalervo
authors.initials: HK
authors.lastname: Väänänen
mesh_terms: D000135:Acid Phosphatase / Q000097:blood* / Q000737:chemistry; D000818:Animals; D015415:Biomarkers / Q000097:blood; D001862:Bone Resorption / Q000097:blood / Q000201:enzymology; D002118:Calcium / Q000097:blood*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000097:blood* / Q000737:chemistry; D046911:Macromolecular Substances; D010010:Osteoclasts / Q000201:enzymology; D051381:Rats; D017382:Reactive Oxygen Species / Q000097:blood; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D000071681:Tartrate-Resistant Acid Phosphatase; D000511:alpha-Macroglobulins / Q000737:chemistry / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D007527:Isoenzymes; D046911:Macromolecular Substances; D017382:Reactive Oxygen Species; D011994:Recombinant Proteins; D000511:alpha-Macroglobulins; C000605510:ACP5 protein, human; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D002118:Calcium