Development of enzymes of adenine nucleotide metabolism in rat brain and liver.

The developmental changes in the activity of certain representative enzymes of adenine nucleotide metabolism, namely AMP deaminase, adenylate kinase and creatine kinase, have been studied in rat brain and liver. The principal points observed can be summarised as follows. (1) Fetal liver has a remarkably high AMP deaminase activity, which decreases immediately after birth. (2) The activities of both soluble and mitochondrial forms of brain creatine kinase are about 50-fold those of liver. The activities of these liver enzymes remain unchanged during the developmental period. In brain, however, these enzymes increase their activities about 3 and 5 times in the cytoplasmic and mitochondrial fractions, respectively. (3) The brain adenylate kinase activity from cytoplasmic fractions increased 4-fold during the 10- and 30-day period, whereas the enzyme from mitochondrial fractions remained unchanged.