The influence of chloride and other univalent inorganic anions on the visible-absorption spectrum of aspartate aminotransferase

Abstract

1. The influence of Cl−, Br−, NO3− and F− ions on the visible-absorption spectrum of deionized aspartate aminotransferase was investigated. 2. Except for F−, these anions caused an increase of the extinction at 430mμ with a concomitant decrease of that at 362mμ. 3. The affinity constants for Cl− and NO3− ions were calculated by a procedure based on the assumption that the anion stabilizes the protonated form of the enzyme chromophore (λmax. 430mμ). 4. The true pK of the chromophore of the enzyme was found to be 5·25.