Comparative analyses of lactic and malic dehydrogenases and their multiple molecular forms in milk from various animal species and man

1. 1. Lactic and malic dehydrogenase levels and isoenzymes have been demonstrated in milk from nine animal species and man. 2. 2. The enzyme activities, at least those of LDH, exhibit an approximately inverse relation to the body size of the species studied. 3. 3. The LDH and MDH isoenzymes in milk show characteristic electrophoretic patterns for different species and for different stages of the lactation period. 4. 4. The results show that LDH and MDH in milk are probably synthesized in the mammary gland. 5. 5. The characteristic behaviour of the isoenzymes in milk may reflect metabolic processes or indicate different types of secretion in the mammary glands of the different species. Participation of enzyme inhibitors or activators in the milk cannot, however, be excluded.