BIOCHEMICAL-CHARACTERIZATION OF THE MOUSE MUSCLE-SPECIFIC ENOLASE - DEVELOPMENTAL-CHANGES IN ELECTROPHORETIC VARIANTS AND SELECTIVE BINDINGTO OTHER PROTEINS

The glycolytic enzyme enolase (EC 4.2.1.11) is active as dimers formed from three subunits encoded by different genes, The embryonic alpha a lpha isoform remains distributed in many adult cell types, whereas a t ransition towards beta beta and gamma gamma isoforms occurs in striate d muscle cells and neurons respectively. It is not understood why enol ase exhibits tissue-specific isoforms with very close functional prope rties. We approached this problem by the purification of native beta b eta-enolase from mouse hindlimb muscles and by raising specific antibo dies of high titre against this protein. These reagents have been usef ul in revealing a heterogeneity of the beta-enolase subunit that chang es with in vivo and in vitro maturation. A basic carboxypeptidase appe ars to be involved in generating an acidic beta-enolase variant, and m ay regulate plasminogen binding by this subunit. We show for the first time that pure beta beta-enolase binds with high affinity the adjacen t enzymes in the glycolytic pathway (pyruvate kinase and phosphoglycer ate mutase), favouring the hypothesis that these three enzymes form a functional glycolytic segment. beta beta-Enolase binds with high affin ity sarcomeric troponin but not actin and tropomyosin. Some of these b inding properties are shared by the alpha alpha-isoenolase, which is a lso expressed in striated muscle, but not by the neuron-specific gamma gamma-enolase. These results support the idea that specific interacti ons with macromolecules will address muscle enolase isoforms at the su bcellular site where ATP, produced through glycolysis, is most needed for contraction. Such a specific targeting could be modulated by post- translational modifications.