The Increasing Adenine Nucleotide Concentration and the Maturation of Rat Liver Mitochondria during Neonatal Development

The levels of adenosine triphosphate, diphosphate, and monophosphate in liver and isolated liver mitochondria were examined in foetal, neonatal, and suckling rats. It was shown that while the total adenine nucleotide level in liver varied only slightly during development, there was a steady increase in the concentration of mitochondrial adenine nucleotides. This increase was most dramatic just after birth. Experiments using pups obtained by caesarean section one day prior to normal birth and kept in a humidicrib for up to two hours, showed that the mitochondrial adenine nucleotide level doubles during this period. This increase is associated with the maturation of the mitochondrial inner membrane as measured by the enhancement of respiratory control.
The results indicate that in addition to the adenine nucleotide translocator—which effects the exchange of adenosine triphosphate and diphosphate—there must be a second transport mechanism present, at least in perinatal mitochondria, which is responsible for the net uptake of adenine nucleotides.
The adenine nucleotides in this study were measured, using a modified luciferin—luciferase assay. In this method the preincubation of sample with appropriate enzymes to convert adenosine monophosphate and diphosphate to adenosine triphosphate, was carried out in the same scintillation vial as the final assay. This eliminated a second sampling step and thereby increased the convenience, speed, and accuracy of this very sensitive method.