Effects of Potassium Iodide on Aspartate Aminotransferase

The absorption spectrum of the phosphopyridoxal form of the enzyme, aspartate aminotransferase, can be perturbed by the anion iodide over a wide range of pH values.The binding of this anion to the catalytic site of the enzyme brings about a decrease in the absorption at 360 nm and a concomitant increase in the absorption band centered at 430 nm corresponding to the positively charged nitrogen of the aldimine linkage of the cofactor.The absorption spectral changes are accompanied by variations in the fluorescence intensity emitted by the cofactor. The fluorescence studies reveal an efficient collisional interaction between the excited state of pyridoxal‐5‐P and the perturbing anion iodide. It is proposed that the active site of the enzyme aspartate aminotransferase is very accessible to the anion iodide.