pH-dependent amino acid induced conformational changes of rabbit muscle pyruvate kinase

The interactions of L-Phe and L-Ala with rabbit muscle pyruvate kinase dependend upon the nature of divalent metal ions sutdied: Mg(II), Co(II), Mn(II), and Ni(II). L-phe inhibited all metal derivatives of the enzyme except Mn(II)--enzyme. L-Ala inhibited only Ni(II)--enzyme and had no effect on other metal derivatives. The inhibition by L-Phe could be partially or completely reversed by L-Ala for all metal derivatives. The mode of inhibition of pyruvate kinase by L-Phe depended upon pH as well as the nature of activating divalent metal ions. The sigmoidal response increased with increasing pH for all metal derivatives inhibited by L-Phe. L-Phe and L-Ala strongly perturbed the coordination sphere of enzyme bound Co(II), but not Ni(II). There were poor correlations between visible circular dichroic (cd) spectral changes and the corresponding kinetic changes. However, L-Phe and (or) L-Ala induced ultraviolet cd and difference absorption spectral changes, on the other hand, corresponded remarkably well with the kinetic observations.