Ground-state electronic destabilization via hyperconjugation in aspartate aminotransferase.
Binding isotope effects for l-aspartate reacting with the inactive K258A mutant
of PLP-dependent aspartate aminotransferase to give a stable external aldimine
intermediate are reported. They provide direct evidence for electronic
ground-state destabilization via hyperconjugation. The smaller equilibrium
isotope effect with deazaPLP-reconstituted K258A indicates that the pyridine
nitrogen plays an important role in labilizing the Cα-H bond.