The pH-induced reversible dissociation of pigeon liver malic enzyme (EC 1.1.1.40) was studied by combined use of chemical cross-linking and SDS/polyacrylamide-gel electrophoresis. The tetrameric enzyme showed a pH-dependent dissociation in an acidic environment. At pH values above 8.0 most molecules existed as tetramers. The enzyme was gradually dissociated at lower pH. When the pH was below 5.0 most of the enzyme was present as the monomeric forms. Reassociation of the subunits was accomplished by adjusting the pH to neutrality. The dissociation and reassociation were almost instantaneous. No trimer was detected. The pigeon liver malic enzyme was thus shown to have a double-dimer quaternary structure with D2 symmetry. In the presence of substrates, the monomer-dimer-tetramer equilibrium favours the direction of dissociation. Tartronate, an L-malate analogue, was found to be more effective than L-malate in this process. When the monomeric forms were immobilized, the enzyme subunits were found to be fully active in catalysis. A possible arrangement of the four identical subunits of the enzyme molecule is proposed to account for the results obtained in this investigation. The origin of the half-of-the-sites reactivity of pigeon liver malic enzyme is also discussed.
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Research Article|
August 15 1988
Reversible dissociation of the catalytically active subunits of pigeon liver malic enzyme
G G Chang;
G G Chang
1Department of Biochemistry, National Defense Medical Center, P.O. Box 8244, Taipei, Taiwan, Republic of China.
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T M Huang;
T M Huang
1Department of Biochemistry, National Defense Medical Center, P.O. Box 8244, Taipei, Taiwan, Republic of China.
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T C Chang
T C Chang
1Department of Biochemistry, National Defense Medical Center, P.O. Box 8244, Taipei, Taiwan, Republic of China.
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Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1988 London: The Biochemical Society
1988
Biochem J (1988) 254 (1): 123–130.
Citation
G G Chang, T M Huang, T C Chang; Reversible dissociation of the catalytically active subunits of pigeon liver malic enzyme. Biochem J 15 August 1988; 254 (1): 123–130. doi: https://doi.org/10.1042/bj2540123
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