Anurans show a distinct dichotomy among the sources of energy they use during larval growth and development, including both endotrophic and exotrophic, which allow studies of the nutritional needs in these different stages. In spite of its swimming function, during the last stages of metamorphosis, the tail releases nutrients necessary for the morphophysiological transformations of the aquatic larval stage into terrestrial adults, during which the animals do not eat, and enzymes play an indispensable role in this process. Alkaline phosphatase is an important enzyme in the mobilization of phosphate required for the anabolism of biomolecules essential to life, whereas acid phosphatase is a lysosomal marker. Thus, the aim of this study was to evaluate the activity of acid and alkaline phosphatases obtained from the tail of bullfrog’s tadpoles (Lithobates catesbeianus), to provide information about the process of nutrient mobilization during development and metamorphosis. Acid and alkaline phosphatase activity increased during metamorphosis, and their highest activities were 189.9 (stage 45) for acid and 39.5 U.mg−1 (stage 44/2) for alkaline phosphatase. The increase in the phosphatases’ specific activities during metamorphosis suggests that the enzymes play a key role in the release of the phosphate needed for the morphophysiological changes that occur during metamorphosis, aside from its importance in tail absorption and cell death. The possibility that the “phosphate regulon system” modulated by phosphate may be conserved in anuran metamorphic tail cells is discussed.

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