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JBC, Vol. 250, Issue 21, 8564-8568, Nov, 1975
I. Cournil, J. M. Barba, D. Verge and M. Arrio-Dupont
Frontal and zonal analysis of the chromatography of aspartate
aminotransferase (EC2.61.1), pig heart cytosolic enzyme, on Bio-Gel P150
shows that holo- and apoenzyme can dissociate at pH 8.3.
Ultracentrifugation and fluorescence depolarization confirm this result.
Kinetic analysis of the fluorescence depolarization experiments favors a
biphasic phenomenon: a few minutes for the faster one and several hours for
the slower one. The apparent dissociation constant is 0.8 muM for the
apoenzyme and 0.18 muM for the pyridoxal 5'-phosphate form of the
holoenzyme. In the presence of sucrose or 0.1 M L-aspartate or a mixture of
70 mM L-glutamate and 2 mM alpha-ketoglutarate, the holoenzyme is dimeric
at concentrations higher than 5 nM. The addition of a mixture of the
substrates L-glutamate and alpha-ketoglutarate to a monomeric holoenzyme
leads to dimerization. The stability of the dimeric form is in the order:
holoenzyme + substrates greater than apoenzyme.
Dissociation of aspartate aminotransferase into subunits. Effect of ligands upon this dissociation
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