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

Abstract

Conformational studies of pyridoxal-5′-phosphate stable adducts with amino acids were performed using Hartree–Fock ab initio (3-21G) and semi-empirical (AM1, PM3) calculations. Conformational energy surfaces versus torsional angles for PLP complexes with glycine, valine, tyrosine, and tryptophan were calculated. Two conformational states (another two are symmetrical relative to the ring), differed by carboxyl group orientation with regard to pyridine cycle, were found for stable adducts of PLP with aliphatic amino acids. 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 fluorescence data, a possible scheme of excited states deactivation of PLP-amino acid stable adducts is suggested.