Human tartrate-resistant acid phosphatase becomes an effective ATPase upon proteolytic activation.
Proteolytic cleavage in an exposed loop of human tartrate-resistant acid phosphatase (TRAcP) with trypsin leads to a significant increase in activity. At each pH value between 3.25 and 8.0 the cleaved enzyme is more active. Substrate specificity is also influenced by proteolysis. Only the cleaved form is able to hydrolyze unactivated substrates efficiently, and at pH >6 cleaved TRAcP acquires a marked preference for ATP. The cleaved enzyme also has altered sensitivity to inhibitors. Interestingly, the magnitude and mode of inhibition by fluoride depends not only on the proteolytic state but also pH. The combined kinetic data imply a role of the loop residue D158 in catalysis in the cleaved enzyme. Notably, at low pH this residue may act as a proton donor for the leaving group. In this respect the mechanism of cleaved TRAcP resembles that of sweet potato purple acid phosphatase.
Mitić
Natasa
N
School of Molecular and Microbial Sciences, The University of Queensland, St. Lucia, Australia.
Valizadeh
Mohsen
M
Leung
Eleanor W W
EW
de Jersey
John
J
Hamilton
Susan
S
Hume
David A
DA
Cassady
A Ian
AI
Schenk
Gerhard
G
D000135:Acid Phosphatase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000251:Adenosine Triphosphatases; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005459:Fluorides / Q000494:pharmacology; D006493:Heparin / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D000071681:Tartrate-Resistant Acid Phosphatase; D014357:Trypsin / Q000378:metabolism
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D006493:Heparin; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D014357:Trypsin; D000251:Adenosine Triphosphatases; D005459:Fluorides