[Characterization and behaviour of lysosomal enzymes in tail tissue of xenopus larvae during involution]

1. The distribution of lysosomal enzymes obtained by density gradient centrifugation of cell-free extracts of Xenopus tail tissue was compared during growth and involution. The particles containing lysosomal enzymes were also characterized by means of electron microscopy. 2. Cytochromeoxidase is recovered to more than 90% in bound form (mitochondria), whereas lysosomal enzymes are characterized by a high proportion of soluble activity (up to 67%). The particle-bound activity ofβ-glucuronidase, cathepsin, and acid RNase show two peaks after centrifugation, in contrast to the activity of acid phosphatase, which is distributed over the whole gradient. During tail involution an increasing proportion of soluble activity is observed, especially for cathepsin and acid RNase. 3. Electronmicroscopical examination reveals a rather heterogeneous composition of the particle populations obtained by density gradient centrifugation. In fractions with highest activity of lysosomal enzymes various types of electron dense granules are found, thus precluding characterization of a specific lysosomal structure. 4. The distribution of enzymes after induction of tail involution with thyroxine was almost similar to the results obtained from spontaneously metamorphosing animals. Since actinomycin D inhibits the increase in lysosomal enzymes and tissue involution it is concluded that the synthesis of soluble acid hydrolases is a prerequisite of hormonal induced tissue involution.