POSTNATAL DEVELOPMENT OF ADENOSINE TRIPHOSPHATASES IN RED AND WHITE RAT MUSCLES

1. The activity of the Mg2⊕-activated ATPase at low ionic strength of rat myofibrils increases 4 times within the first 3 weeks of postnatal development. The activity of the Ca2⊕-activated ATPase at high ionic strength and pH 9 (myosin type ATPase) increases twofold during the same period. 2. With further development up to the adult age no differences in the enzymatic activities become apparent between myofibrils from red and white muscles. But the Mg2⊕-activated ATPase of myofibrils of white muscles is more sensitive to heat inactivation. 3. The EGT A sensitivity which reflects the function of troponin and tropomyosin, increases not only in the early postnatal period but up to the adult age. © 1968, Walter de Gruyter. All rights reserved.