Developmental changes in heart and muscle phosphofructokinase isozymes.
Phosphofructokinase isozymes of fetal, neonatal, and adult rat heart and skeletal muscle were characterized by DEAE-cellulose chromatography, agarose gel electrophoresis, and immunodiffusion with specific antisera. The results of these studies indicate that in skeletal muscle and heart the levels of the major liver phosphofructokinase isozyme (PFK-L2) and the muscle phosphofructokinase isozyme (PFK-M) are dependent on the developmental status of the rat. For example, PFK-L2 and PFK-M are present in fetal and early neonatal skeletal muscle; whereas in adult skeletal muscle, only PFK-M is detectable. By DEAE- cellulose chromatography, PFK-L2 activity was estimated to be 2.4 units/g (41% of total phosphofructokinase activity) in fetal muscle, very low and not resolved from PFK-M in 7-day neonatal muscle, and not detectable in adult muscle. Further, PFK-M activity was found to be 3.4 units/g (59% of total phosphofructokinase activity), 10 units/g, and 31.6 units/g in fetal, 7-day neonatal, and adult skeletal muscle, respectively. The developmental changes of heart phosphofructokinase isozymes differ considerably from that of the skeletal muscle phosphofructokinase isozymes. In fetal heart, PFK-L2 is the major phosphofructokinase isozyme (5.6 units/g), constituting 67% of total phosphofructokinase activity. Further, in fetal heart another phosphofructokinase isozyme (33% of total phosphofructokinase activity) was found by DEAE-cellulose chromatography which is different from PFK-M and PFK-L2. In 7-day neonatal and adult heart, PFK-M and PFK-L2 are the only detectable phosphofructokinase isozymes. Varying from 5.6 units/g (44% of total) in 7-day neonatal to 5.9 units/g (40% of total) in adult heart, PFK-L2 activity remains fairly constant. Also, PFK-M is very low in fetal heart but increases within 1 week postpartum to 5.5 units/g (50% of total activity) and to 8.9 units/g (60% of total activity) in adult heart.