[Diagnosis of genetically determined diseases]

Enzymopathies of pyruvate kinase are caused by defects of structural genes forming stable and unstable mutants, respectively. Stable mutants of PK are characterized by high S0,5 PEP and nearly unchanged Vmax. A decrease of PEP affinity can be the result from a very high allosteric constant L0 or from an increased KPEP. From the pattern of PAGE can be concluded that stable PK mutants are tetraheteromers composed of two normal and two shortened polypeptide chains. We suppose that this is the result of a mutation of a codon which stops the polypeptide synthesis of PK earlier. Most PK mutants are unstable. They are characterized by low catalytic activity and high PEP affinity. The kinetic properties of unstable mutants are changed posttranslational by proteolytic modifications. Furthermore low S0,5 PEP values result from a persistence of the isoenzyme PK-K in reticulocytes and erythrocytes, respectively. A prenatal diagnosis of PK enzymopathies can be carried out with a very small blood volume by using the method of isoelectrophoretic focussing.