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  • Title: Characterization of monomeric 4-aminobutyrate aminotransferase at low pH.
    Author: Pineda T, Osei YD, Churchich JE.
    Journal: Eur J Biochem; 1995 Mar 15; 228(3):683-8. PubMed ID: 7737164.
    Abstract:
    4-Aminobutyrate aminotransferase undergoes a reversible process of association/dissociation at low pH. At pH 5.0, monomeric species exist predominantly in solution as revealed by FPLC and time-dependent emission anisotropy measurements. The observed rotational correlation time at pH 5.0, phi obs = 25 ns, corresponds to a compact spherical unit of 52 kDa. An increase in the net charge of the macromolecule at pH 5.0 is responsible for destabilization of the dimeric structure, (WEL approximately 41.84 kJ/mol), but the dissociation of the protein does not perturb the secondary structure as revealed by CD measurements. The fluorescent probe 1-anilinonaphthalene-8-sulfonate (ANS), bound to hydrophobic sites of the enzyme, was used to monitor the kinetics of protein dissociation by stopped-flow spectroscopy. The dissociation of the dimeric structure at pH 5.0 was characterized by a relaxation time of 18 ms. The rate of association of monomeric subunits at pH 7.0 was too fast to be detected in the stopped-flow instrument. These observations have some bearing on the mechanism of reconstitution of dimeric structures of 4-aminobutyrate aminotransferase in the cell.
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