The specificity of the histochemical method for adenosine triphosphatase (ATPase) has been investigated. ATPase is classified as a substrate-specific enzyme, but other phosphatases may also act on ATP. The histochemical method introduced by Glick and Fischer was initially considered limited due to the action of phosphomonoesterase on ATP at alkaline pH. However, subsequent studies supported its validity when ATP staining occurred in areas not reactive with phosphomonoesters. The study used a medium similar to Gomori's to investigate ATPase activity, focusing on the relationship between the sulfhydryl (-SH) group and ATPase and phosphomonoesterase activities. Skeletal muscle ATPase was shown to require -SH groups for activity. Reversible inhibition of ATPase activity was achieved in cardiac, skeletal, and kidney tissues using -SH inhibitors and activators. Alkaline phosphatase was inhibited by -SH compounds, allowing control of its interference in ATP dephosphorylation. The study demonstrated that ATPase activity is distinct from other phosphatases, with alkaline phosphatase contributing to ATP dephosphorylation. The histochemical test for ATPase gained new significance with these findings. The study compared the localization of phosphatase activity toward ATP, ADP, and A-5-P in various tissues, showing differences in staining patterns. The results indicated that ATPase activity is localized in specific cellular structures, such as myofibrils and mitochondria, while other phosphatases showed different reactivity. The study also showed that -SH compounds like BAL and cysteine could enhance or inhibit phosphatase activity, depending on the substrate. The findings suggest that ATPase activity is more specific than previously thought, with -SH groups playing a crucial role in its function. The study concluded that the histochemical method for ATPase is specific, with -SH-dependent ATPase activity being distinguishable from other phosphatases. The results highlight the importance of -SH groups in ATPase activity and the role of alkaline phosphatase in ATP dephosphorylation. The study also demonstrated the differences in phosphatase activity localization in various tissues, emphasizing the specificity of the histochemical method for ATPase.The specificity of the histochemical method for adenosine triphosphatase (ATPase) has been investigated. ATPase is classified as a substrate-specific enzyme, but other phosphatases may also act on ATP. The histochemical method introduced by Glick and Fischer was initially considered limited due to the action of phosphomonoesterase on ATP at alkaline pH. However, subsequent studies supported its validity when ATP staining occurred in areas not reactive with phosphomonoesters. The study used a medium similar to Gomori's to investigate ATPase activity, focusing on the relationship between the sulfhydryl (-SH) group and ATPase and phosphomonoesterase activities. Skeletal muscle ATPase was shown to require -SH groups for activity. Reversible inhibition of ATPase activity was achieved in cardiac, skeletal, and kidney tissues using -SH inhibitors and activators. Alkaline phosphatase was inhibited by -SH compounds, allowing control of its interference in ATP dephosphorylation. The study demonstrated that ATPase activity is distinct from other phosphatases, with alkaline phosphatase contributing to ATP dephosphorylation. The histochemical test for ATPase gained new significance with these findings. The study compared the localization of phosphatase activity toward ATP, ADP, and A-5-P in various tissues, showing differences in staining patterns. The results indicated that ATPase activity is localized in specific cellular structures, such as myofibrils and mitochondria, while other phosphatases showed different reactivity. The study also showed that -SH compounds like BAL and cysteine could enhance or inhibit phosphatase activity, depending on the substrate. The findings suggest that ATPase activity is more specific than previously thought, with -SH groups playing a crucial role in its function. The study concluded that the histochemical method for ATPase is specific, with -SH-dependent ATPase activity being distinguishable from other phosphatases. The results highlight the importance of -SH groups in ATPase activity and the role of alkaline phosphatase in ATP dephosphorylation. The study also demonstrated the differences in phosphatase activity localization in various tissues, emphasizing the specificity of the histochemical method for ATPase.