Effects Of Small Ions Research Articles

On the effect of small ions on the activity of glutamic-aspartic transaminase

A kinetic study of glutamic-aspartic transaminase confirmed the following mechanism of action: enzyme-pyridoxal phosphate + aspartate ⇌ enzyme-substrate complexes I⇌enzyme-pyridoxamine + oxaloacetateenzyme-pyridoxamine + ketoglutarate ⇌ enzyme-substrate complexes II⇌enzyme-pyridoxal + glutamate Maximal velocities and turnover numbers of the forward and backward reactions, and affinity constants for the four substrates, were calculated from steady-state kinetic data. It was shown that several ions exert a partially competitive activation towards four carbon substrates. These data and the observation that substrate amounts of the pyridoxal form of the enzyme react reversibly with alanine and that catalytic amounts of the enzyme catalyze the reversible transamination between alanine and ketoglutarate but not between alanine and oxaloacetate point to the possible existence, besides the coenzyme, of two active sites, one for oxaloacetate and aspartate, the other for ketoglutarate and glutamate.