Abstract
Summary: The isozymic composition of phosphofructokinase (EC. 2.7.1.11) from human fetal tissues has been investigated by immunological characterization, electrophoresis, purification, and SDS-polyacrylamide gel electrophoresis of the dissociated subunits.
One of the characteristics of fetal tissues is the indiscriminate expression by all the cells of two or three of the basic forms of phosphofructokinase without any isozyme really corresponding to a specifically fetal form. In particular, L-type enzyme, identical to the highly regulatory enzyme synthesized by the adult hepatocytes, is found in most fetal tissues, especially in muscle and brain. M-type subunits are also detected in most of the organs and constitute the major form in fetal muscle and adrenals. F-type subunits are predominant in fetal stomach and yolk sack and are practically the only form in fetal heart.
Some electrophoretic and chromatographic differences between fetal and adult M-type phosphofructokinase exist; whether their nature is genetic or posttraductional is so far unknown.
Some differences (of molecular weight and chromatographic properties) are also detected between the fetal L-type subunits and enzyme from adult granulocytes. A mild proteolytic attack of the former by subtilisin transforms it into an enzyme form indistinguishable from granulocyte phosphofructokinase.
Speculation: In the fetus as well as in adult tissue, phosphofructokinase could be coded by a three-gene-system, coding for the M, L, and F subunits. The M and L subunits could undergo some postsynthetic changes, increasing the heterogeneity of phosphofructokinase in the various tissues.
One of the characteristics of the “fetal state” could be the indiscriminate expression of several of the basic genes; differenciation would be associated with the selective repression of the “unuseful” forms. It is expected that in cancer a reappearance of the normally repressed forms would occur.
Phosphofructokinase differs, therefore, from other enzymes which p ssess forms expressed in all tissues in the fetal period and have tissue-specific isozymes that appear later. These isozymes (like liver aldolase and muscle creatine kinase) are strong tissue markers, whereas phosphofructokinase isozymes appear to be weak tissue markers.
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Kahn, A., Cottreau, D. & Dreyfus, J. Phosphofructokinase in Human Fetus. Pediatr Res 14, 1162–1167 (1980). https://doi.org/10.1203/00006450-198011000-00003
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DOI: https://doi.org/10.1203/00006450-198011000-00003