Activity and localization of acid hydrolases in the dorsal tail fin of Rana pipiens during metamorphosis

The specific and total activities of acid phosphatase (AcP), hyaluronidase (HU), β‐N‐acetylglucosaminidase (NAG) and lactate dehydrogenase (LDH) of tail fin are constant during prometamorphosis. During climax, as the fin is resorbed, the activities of the hydrolases increase while the specific activity of LDH remains constant and the total activity decreases. The apparent Km and pH optimum of the hydrolases are the same at prometamorphosis and climax. Similar changes in enzyme activities are found in pieces of prometamorphic fin induced to resorb in vitro by thyroxine treatment. AcP, NAG and LDH are found, but in different proportions, in both fragments of prometamorphic fins separated into epidermis and mesenchymal core. NAG and LDH are more concentrated in the epidermis while AcP is more concentrated in the core. A higher percentage of NAG and AcP activity is found in the mitochondrial‐lysosomal and supernatant subcellular fractions at climax than at prometamorphosis. In addition, the specific activities of these enzymes are higher in the mitochondrial‐lysosomal and supernatant fractions at climax while the specific activity and subcellular distribution of LDH is constant. The increase in activity of the hydrolases of the fin which occurs in synchrony with resorption during spontaneous metamorphosis or that induced in vitro by thyroxine suggests that these events are related and that the hydrolases are concerned with the degradation of the connective tissues of the fin during regression.