Assignment of the human gene for liver-type 6-phosphofructokinase isozyme (PFKL) to chromosome 21 by using somatic cell hybrids and monoclonal anti-L antibody.

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Human 6-phosphofructokinase (PFK; ATP:D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) is under the control of structural loci that code for muscle (M), liver (L), and platelet (P) subunits, which are variably expressed in different tissues; human diploid fibroblasts and leukocytes express all three genes. Random tetramerization of these subunits produces various isozymes, which can be distinguished from one another by ion exchange chromatography or by subunit-specific monoclonal antibodies. We have examined 17 somatic cell hybrids established between Chinese hamster cells and human diploid fibroblasts or leukocytes for the expression of L-type subunits of human PFK. As electrophoresis does not distinguish between Chinese hamster PFKs and human PFKs, we used an anti-human L-subunit-specific monoclonal antibody, which does not react with chinese hamster PFKs. The expression of human L subunits in the hybrids was detected by the enzyme-immunoprecipitation technique using staphylococci bearing protein A as an immunoadsorbent. Twelve out of 17 hybrids expressed human L subunits and retained chromosome 21, as determined by chromosome and isozyme marker analysis, whereas 5 did not express human PFKL and lacked chromosome 21. The mean erythrocyte PFK of seven individuals with trisomy 21 was found to be elevated (147% of normal). A specific increase in L subunits in trisomic erythrocytes was evident chromatographically by a striking increase in L4 species (50%; normal 10%) and immunologically by decreased precipitation with anti-M monoclonal antibody (50%; normal 80%). We conclude from these data that PFKL is located on chromosome 21 and that the previously noted elevation of erythrocyte PFK activity in individuals with trisomy 21 is due to a gene-dosage effect.

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