Tartrate-resistant acid phosphatase (TRAP, also called TRACP) and alkaline phosphatase (ALP) are osteoclast and osteoblast enzyme markers, respectively, that are involved in bone metabolism. Takara's TRAP & ALP Assay Kit allows for the simultaneous detection of both ACP (acid phosphatase) and ALP (alkaline phosphatase) enzymes via pNPP (p-nitro-phenyl phosphate) substrate. The addition of tartaric acid into the ACP assay allows for differentiation of TRAP from ALP activity. Because the TRAP and ALP Assay Kit utilizes an aqueous substrate, quantification of enzyme activities can be accomplished quickly by measuring the absorbance of the reactant. An alternative option is the TRAP & ALP Double-Stain Kit (Cat. #MK300), which contains a non-soluble substrate suitable for simultaneous cell staining of alkaline and acid phosphatase activities. Either kit may be selected depending on user interest.