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Abstract We describe the use of sodium thymolphthalein monophosphate as a substrate for measuring acid phosphatase activity in serum. Thymolphthalein is liberated in the reaction and is conveniently measured by increasing the pH of the medium, which produces a color and also stops the hydrolysis. Optimal conditions for enzymatic activity were defined for use in the final assay system. Purified acid phosphatase isoenzymes from various human tissues and sera from patients with nonprostatic diseases most likely to affect serum acid phosphatase activity were used to show that the new method is more specific for the prostatic enzyme than other commonly used procedures for acid phosphatase. Other advantages include simplicity, good sensitivity over a wide range of activity, high precision, zero-order kinetics to about 200 times the upper limit of normal, easy standardization by a pure standard, and reagent stability.
Roy et al. (Mon,) studied this question.