Pyruvate kinase isozymes in adult and fetal tissues of chicken

Tissues of fetal and adult chickens were examined for pyruvate kinase activity. Two electrophoretically distinguishable and noninterconvertible isozymes were found. One of these, designated as type K (for kidney), is the sole pyruvate kinase in the early fetus and is found in appreciable quantities in all adult tissues except striated muscle. The second isozyme, type M, appears shortly before hatching in striated muscle and brain. These two isozymes correspond in their developmental pattern, tissue distribution, electrophoretic, immunological, and kinetic propertiesto similarly designated mammalian pyruvate kinases. However, no kinetic, immunological, or electrophoretic evidence could be found for a chicken isozyme corresponding to the mammalian type L pyruvate kinase. As the latter isozyme seems to be limited in its distribution mostly to highly differentiated gluconeogenic tissues (notable liver, kidney, and small intestine), our results support the proposition that the mammalian type L pyruvate kinase is a specilized isozyme that is present in mammals but not in birds.