[The behaviour of ninhydrin-positive substances in the tail tissue ofXenopus larvae during growth and metamorphosis].

1. In order to characterize further the biochemical events of tissue resorption in the tadpole tail the pattern of free amino acids and related substances was investigated by using ion-exchange column chromatography of methanol extracts prepared from tails ofXenopus larvae during prometamorphosis and climax. For the purpose of comparison wet and dry weight, content of protein nitrogen and total nitrogen (TN) as well as catheptic activity were also determined. 2. In tails of prometamorphic tadpoles 30 fractions of ninhydrin-positive substances have been found, of which alanine, glutamine-asparagine, carnosine, lysine, glycine, glutamic acid showed highest concentrations (>50nM/mg TN). Total concentration of ninhydrin-positive substances increases during growth (prometamorphosis), but decreases during early stages of tail involution (climax) without significant qualitative changes. During either period the relative concentrations of individual fractions vary independently of each other. 3. From a comparison with protein and total nitrogen content in tails, it is obvious that high levels of ninhydrin-positive substances are characteristic of growing rather than regressing tail tissues.