Tartrate-resistant acid phosphatase or acid phosphatase 5, tartrate resistant (ACP5 or TRAP) is a glycosylatedmonomericmetalloenzyme expressed in mammals. It has a molecular weight of approximately 35kDa, a basic isoelectric point (7.6-9.5) , and optimal activity in acidic conditions. TRAP is synthesized as latent proenzyme and activated by proteolytic cleavage and reduction. It is differentiated from other mammalian acid phosphatases by its resistance to inhibition by tartrate, molecular weight and characteristic purple colour.
The mechanism of phosphate ester hydrolysis by TRAP is through a nucleophilic attack mechanism,, with conflicting reports for both mechanisms.