Histochemically demonstrable acid phosphotyrosine phosphatase activity in human tissues

A histochemical method for the demonstration of activity of acid phosphatase(s) hydrolyzing o-phospho-L-tyrosine at pH 6.2 is described. Due to the instability of ordinary acid phosphatase incubation media containing phosphotyrosine and lead salt, the latter was dissolved in citrate solution (possibly forming a chelate) to obtain a stable incubation mixture. Localization of enzyme activity at the cellular level was good. Phosphotyrosine is known to be hydrolyzed at slightly acid pH by prostatic, macrophagic, and low-molecular weight cytoplasmic acid phosphatases and phosphotyrosyl protein phosphatases. These enzymes have been suggested or are established to be involved in cellular regulation by dephosphorylation of tyrosyl residues of proteins formed by various protein tyrosine kinases. An unexpected finding from various tissues was that the widely distributed lysosomal acid phosphatase did not contribute to the histochemical reaction, possibly due to poor hydrolysis of phosphotyrosine by lysosomal-type acid phosphatase. Various human tissues were studied for their acid phosphotyrosine phosphatase activities, which were then quantitated photometrically. Highest activity was found in the prostate glands, seminal vesicle epithelium, endometrial secretory glands, alveolar macrophages, stratum granulosum of the skin, and lymph nodes. The contribution of various enzymes hydrolyzing phosphotyrosine to histochemically detected activity in different tissues is discussed here.