Recombinant human and mouse purple acid phosphatases: expression and characterization

K Marshall, K Nash, G Haussman, I Cassady, D Hume, J de Jersey, S Hamilton

Research output: Contribution to journalArticlepeer-review

Abstract

The mammalian purple acid phosphatases (also called tartrate-resistant acid phosphatases) are expressed primarily in actively resorbing osteoclasts and activated macrophages. The enzymes are characterized by the presence of a binuclear iron center at the active site. Recent studies on transgenic mice lacking purple acid phosphatase implicate the osteoclast enzyme in both bone resorption and bone mineralization. To characterize the mammalian enzymes in more detail, particularly with respect to their substrate specificity at the low pH of the osteoclastic resorptive space (2.5-3), we have purified the recombinant human and mouse enzymes from baculovirus-infected insect cells. The properties of the recombinant mouse enzyme are compared with those of the nonrecombinant enzyme isolated from mouse spleen. The kinetics of hydrolysis of the substrates p-nitrophenyl phosphate, phosphotyrosine, and pyrophosphate and a phosphotyrosyl peptide by the recombinant human and mouse enzymes and the nonrecombinant mouse and pig enzymes were analyzed. For all the enzymes the ratio k(cat)/Km was typically approximately 10(6) M(-1) s(-1) and was higher at pH 2.5 than at 4.9. The increase was attributable to a large decrease in Km at the lower pH value. The results indicate that the enzyme exhibits high catalytic efficiency toward substrates such as pyrophosphate and acidic phosphotyrosine-containing peptides, particularly at low pH values typical of the bone resorptive space. The implications of the results for the physiological function of the enzyme are discussed.
Original languageEnglish
Pages (from-to)230-6
Number of pages7
JournalArchives of biochemistry and biophysics
Volume345
Issue number2
DOIs
Publication statusPublished - 15 Sep 1997

Keywords

  • Acid Phosphatase
  • Animals
  • Humans
  • Isoenzymes
  • Kinetics
  • Mice
  • Nucleopolyhedrovirus
  • Oxidation-Reduction
  • Peptide Fragments
  • Recombinant Proteins
  • Sequence Analysis
  • Species Specificity
  • Spodoptera
  • Swine

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