PHOTOPHYSICAL STUDY OF PYRIDOXAL 5'-PHOSPHATE AND ITS SCHIFF-BASE WITH N-HEXYLAMINE

Phosphopyridoxal enzymes exhibit a wide variety of reactions, The acti vation mechanism proceeds with the formation of Schiff bases that unde rgo loss or transfer of one or more protons. Changes in the fluorescen t properties of the pyridoxal 5'-phosphate and its Schiff base may sig nal changes in the protonation state and/or in the microenvironment of the cofactor. In this paper the average fluorescence lifetime of pyri doxal 5'-phosphate (PLP) as a function of pH was studied in a medium o f 0.1 M ionic strength at 25 degrees C. The ionic species of PLP with an unprotonated hydrogen atom were found to exhibit fluorescence lifet imes in the region of 100 ps on excitation at lambda = 390 nm. The ave rage fluorescence lifetimes for PLP in its Schiff bases with n-hexylam ine in media of low polarity are reported.