L-Lysine-α-Ketoglutarate ε-Aminotransferase<subtitle>Properties of the Bound Pyridoxal 5′-Phosphate</subtitle>

Abstract

L-Lysine-alpha-ketoglutarate epsilon-aminotransferase of Flavobacterium lutescens (Achromobacter liquidum) IFO 3084 shows positive circular dichroic bands at 340 and 415 nm where absorption maxima are observed, and fluorescence maxima at 380 and 490 nm on excitation at 340 and 415 nm, respectively. The pyridoxal 5'-phosphate absorbing at 415 nm is bound through an aldimine linkage to an epsilon-amino group of the lysine residue of the protein. Upon aging, the 415 nm pyridoxal 5'-phosphate changes to a less active form (lambda max, 325 nm), which is distinguishable from the 340 nm pyridoxal 5'-phosphate. This 325 nm bound pyridoxal 5'-phosphate is reduced with sodium borohydride and shows no circular dichroism. When the semiapoenzyme is aged under the same conditions, no spectral change is observed. These findings suggest that the pyridoxal 5'-phosphate bound through an aldimine linkage may be converted into a carbinol amine or some other related form by aging.