In order to elaborate some general correlations between metabolic pathways and morphogenetic events the activity-profiles of the enzymes GAPDH, LDH, CE, MDH, GOT, G-6-PDH, and 6-PGDH have been determined in different developmental stages. Unusually high activities of these enzymes could be extracted from unfertilized eggs. In the course of embryogenesis and metamorphosis two metabolic patterns alternate repeatedly. The first pattern is characterized by a relatively low glycolytic potency (low GAPDH- and LDH-levels) connected with a relatively high oxidative capacity (low ratio of GAPDH/CE and rising O-consumption). This pattern, which indicates the predominance of energy production, is realized during cleavage and during the phase of contraction at the onset of metamorphosis. The second metabolic pattern combines high glycolytic potency (high GAPDH- and LDH-levels) with a high ratio of GAPDH/CE. This predominance of anaeroblic metabolism is correlated with high activities of MDH and GOT. An important portion of the substrate-flux may be directed towards anabolic processes. This metabolic condition is found during gastrulation and during the middle phase of metamorphosis: stages in which differentiation is initiated. This repeated change in the main metabolic behavior is also reflected by the operation of the pentose-phosphate-cycle. The activities of G-6-PDH and 6-PGDH decrease during cleavage and during early metamorphosis and increase during the differentiation of the planula and of the primary polyp. In the fully developed polyp, however, the 6-PGDH-activity disappears whilst that of the G-6-PDH remains high. 2. The induction of metamorphosis which normally is brought about by a bacterial agent and artificially by a Cs-pulse, is characterized by an enhanced activity of the Na\t-K-ATPase. The maximum activity could be measured in homogenates and in living larvae 2 hrs and 0.5\2-1.5 hrs respectively after the application of Cs. This finding supports the hypothesis that cation carriers are involved in the larval response to inductive stimuli. The induced peak of activity, in early metamorphosis, is followed by a second peak occurring spontaneously 3-4 hrs later. Relatively high ouabain-sensitive as well as ouabaininsensitive ATPase activities could also be observed in homogenates of young embryos.
