[Changes in the isoenzyme spectrum of several oxyreductases during rat ontogenesis].

Studies have been made on changes in isoenzymic spectra of lactate (LDH), malate (MDH) and sorbitol (SDH) dehydrogenases from the liver and blood serum of growing rats. In the blood serum of adult animals, 5 isoenzymes of LDH, 2 isoenzymes of MDH and 2 isoenzymes of SDH were found; in liver extracts 5, 6 and 7 fractions were observed correspondingly. During the development, relative amount of H-type isoenzymes LDH increases, whereas isoenzymic spectra of MDH and SDH undergo quantitative and qualitative changes. In ontogenesis, the specific activity of all the enzymes investigated increased. The initial level of LDH in foetal liver was higher than in adult animals, that of MDH and SDH - lower. Beginning from the 2nd week of postnatal life, the activity of LDH in the liver decreased up to the level typical of adult animals; the activity of MDH and SDH in the liver increased.