Microspectrophotometric studies on single crystals of the tryptophan synthase alpha 2 beta 2 complex demonstrate formation of enzyme-substrate intermediates.

摘要: Abstract Microspectrophotometry of single crystals the tryptophan synthase alpha 2 beta complex from Salmonella typhimurium is used to compare catalytic and regulatory properties enzyme in soluble crystalline states. Polarized absorption spectra demonstrate that chromophoric intermediates are formed between pyridoxal phosphate at active site subunit added substrates, substrate analogs, reaction intermediate analogs. Although forms produce some same enzyme-substrate intermediates, including Schiff base quinonoid cases equilibrium distribution these differs two states enzyme. Ligands which bind alter both The three-dimensional structures a derivative with indole-3-propanol bound have recently been reported (Hyde, C. C., Ahmed, S. A., Padlan, E. Miles, W., Davies, D. R. (1988) J. Biol. Chem. 264, 17857-17871). Our present findings help establish experimental conditions for selecting defined future x-ray crystallographic analysis ligands sites subunits. These studies should explain how catalysis occurs binding ligand one affects other 25 A away.