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Erythrocyte pyruvate kinase (PK): The variable significance of “nucleotide specificity” in the characterization of mutant variants
Author(s) -
Valentine W. N.,
Paglia D. E.,
Nakatani M.,
Brockway R. A.
Publication year - 1987
Publication title -
american journal of hematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.456
H-Index - 105
eISSN - 1096-8652
pISSN - 0361-8609
DOI - 10.1002/ajh.2830260408
Subject(s) - pyruvate kinase , mutant , pkm2 , nucleotide , pyruvate kinase deficiency , biology , biochemistry , genetics , enzyme , gene , glycolysis
The half‐saturation constant (K 0.5s ) phosphoenolpyruvate (PEP) for red cell pyruvate kinase (PK) with co‐factors UDP and GDP is less than one‐half that with ADP with or without additions of the allosteric modifier, fructose‐1, 6‐dephosphate (F‐1, 6‐P 2 ) to the assay. The Vmax is markedly greater with ADP than with UDP or GDP, but with (PEP) at 0.5 mM, activity with all co‐factors is about equal and at lower concentrations greater with UDP and GDP. With high K 0.5s (PEP) mutant enzymes, and at the usual test concentration (1mM) for PEP when nucleotide specificity is assessed, the abnormally low saturation of variant enzymes may result in higher activity with UDP and GDP than with ADP–the opposite of the “normal situation.” The apparent aberration in nucleotide specificity may thus be illusory and secondary to the abnormal K 0.5s (PEP) of the mutant. Example data are recorded. Variations in K 0.5s (PEP) may also be introduced during enzyme preparation for assay, particularly when partial purification is employed.