Hemoglobin transition in relation to metamorphosis in normal and isogenicXenopus

Electrophoretic separation of hemoglobins of normalXenopus laevis and of isogenic animals derived from female hybrids ofXenopus laevis×Xenopus gilli revealed 5-9 components in premetamorphic larvae, and 3-4 components in adult toads. InXenopus laevis the number of larval hemoglobin components showed considerable variation, but this variation was absent in isogenic tadpoles, suggesting a genetic basis for hemoglobin polymorphism in larvae.Electrophoretic separation of larval and adult hemoglobins at different concentrations of acrylamide and treatment of these solutions with mercaptoethanol revealed that larval hemoglobin components are charge isomers, whereas adult hemoglobin was found to contain a minor dimeric component.Estimation of hemoglobin components showed that the main increase in adult hemoglobin, i.e from 30-90% of total hemoglobin, occurs within 4 weeks after completion of metamorphosis. By incroporation of³H amino acids in vivo a switch to preferential synthesis of adult hemoglobin and a corresponding decrease in larval hemoglobin production could be demonstrated during early climax stages. This suggests that thyroid hormones are involved in the hemoglobin transition. Yet chemical inhibition of the larval thyroid by thiourea resulted in a delayed but complete hemoglobin transition without morphological transformation. It is concluded that hemoglobin transition and morphological transformation of theXenopus tadpole require different concentrations of thyroid hormones.