Ab initio and semi-empirical conformational studies of pyridoxal-5 '-phosphate derivatives

Conformational studies of pyridoxal-5 ' -phosphate stable adducts with amin o acids were performed using Hartree-Fock ab initio (3-21G) and semi-empiri cal (AM1, PM3) calculations. Conformational energy surfaces versus torsiona l angles for PLP complexes with glycine, valine, tyrosine, and tryptophan w ere calculated. Two conformational states (another two are symmetrical rela tive to the ring), differed by carboxyl group orientation with regard to py ridine cycle, were found for stable adducts of PLP with aliphatic amino aci ds. For complexes of PLP with tyrosine or tryptophan the situation is more complicated due to interaction between pyridine and aromatic rings. On the basis of computational studies results, photochemical and time-resolved flu orescence data, a possible scheme of excited states deactivation of PLP-ami no acid stable adducts is suggested. (C) 2001 Elsevier Science B.V. All rig hts reserved.