Isozyme profiles of lactic dehydrogenase and creatine phosphokinase in neonatal mouse hearts.

Isozyme profiles of lactic dehydrogenase (LDH) and creatine phosphokinase (CPK) were determined in cardiac tissue of mice during postnatal development. LDH isozymes 1 and 5 showed a definite developmental change, achieving the adult values by 20 days of age, while the other three isozymes showed no change. During the first 2 postnatal weeks, a developmental change was seen in the activities of the 'mito' and MB isozymes of CPK, with the adult profile being established by day 20. CPK isozymes MM and BB did not change during this interval.