Physiological relevance of the changing subunit composition and regulatory properties of the 6-phosphofructo-1-kinase isozyme pools during heart and muscle development.
During postnatal development, the subunit compositions of the 6-phosphofructo-1-kinase isozyme pools of heart and skeletal muscle are known to change. The isozyme pools from fetal muscle were composed of the L-type (60%), and M-type (36%) and C-type (4%) subunits and the isozymes from fetal and early neonatal heart contain nearly equal amounts of all three subunits. During postnatal development of both tissues, the proportion of the M-type subunit increases until it is the only type present in adult muscle and the major subunit in adult heart (75%). The isozyme pool from fetal muscle exhibit a decreased affinity for fructose-6-P and a greater susceptibility to ATP inhibition compared to the M-rich isozymes which are subsequently present. The isozyme pools from fetal and early neonatal heart, if compared to the M-rich isozymes which are present later during heart development and to the fetal muscle isozymes, exhibited the least affinity for fructose-6-P and the greatest susceptibility to ATP inhibition. Comparison of the isozyme pools containing little or no C-type subunit with those from fetal and early neonatal heart clearly indicates that the presence of substantial levels of the C-type subunit imposed a decreased ability for fructose-2,6-P2 to both lower affinity for fructose-6-P and antagonize sensitivity to ATP inhibition. Although still not thoroughly appreciated, it appears that the changing nature of the isozyme pools in these tissues permits regulation of glucose metabolism in a manner which allows efficient utilization of nutritional opportunities and which adequately meets the energy requirements of each tissue at different stages of development.
Dunaway
G A
GA
Department of Pharmacology, Southern Illinois University School of Medicine, Springfield 62794-9230.
Kasten
T P
TP
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D005260:Female; D006321:Heart / Q000196:embryology*; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000196:embryology* / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology*; D010770:Phosphotransferases / Q000378:metabolism*; D011247:Pregnancy; D011487:Protein Conformation; D051381:Rats; D011919:Rats, Inbred Strains
D007527:Isoenzymes; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; C022502:pyrophosphate-fructose 6-phosphate 1-phosphotransferase