The Rotational Mobility of Pyridoxamine 5-Phosphate

The technique of fluorescence polarization was used to study the degree of mobility of the cofactor pyridoxamine 5-phosphate bound to the catalytic site of the enzyme aspartate aminotransferase. While the cofactor of the phosphopyridoxamine form of the enzyme exhibits rotational mobility, the pyridoxyl 5-phosphate residues of the reduced enzyme are rigidly bound to the enzyme surface. These results have direct bearing on the question of the functional role played by pyridoxamine 5-phosphate during enzymatic transamination.