CHANGES DURING DEVELOPMENT OF MOUSE BRAIN IN THE ACTIVITIES AND SUBCELLULAR DISTRIBUTIONS OF CREATINE AND ADENYLATE KINASES

— The activities and electrophoretic patterns of creatine (CK) and adenylate (AK) phosphokinases were determined in the mitochondrial and high speed supernatant fractions of developing and adult mouse brain. The CK activity of the cytosol increases three‐fold between 9 and 19 days of age and four‐fold by 29 days. Mitochondrial CK activity increases from birth to reach a maximum four‐fold that at birth by 19 days of age. The developmental changes in soluble AK activity parallels that of CK. Although the increase in CK activity of the mitochondria exceeds that of the mitochondrial proteins during the period of rapid brain development, mitochondrial AK specific activity changes little. No major changes were found during development in the electrophoretic patterns of proteins with CK or AK activity in the supernatant and mitochondrial fractions. The changes in mitochondrial CK and AK activity parallel the change from a predominantly glycolytic to an aerobic mode of brain metabolism and support the concept that these enzymes play an important role in mitochondrial energy metabolism. Soluble CK and AK activity increase concomitant with neuronal maturation and the associated greatly increased need for rapidly available high energy phosphate.