title: Negative cooperativity in tryptophan synthase alpha subunit dissociation is caused by the bound coenzyme: pyridoxal 5'-phosphate.
abstract: Sedimentation equilibrium studies of dilute solutions of tryptophan synthase reveal dissociation from the holoenzyme form, alpha 2 beta 2, into mixtures of alpha beta 2, small amounts of beta 2, and alpha as well as the original alpha 2 beta 2 holoenzyme. The holoenzyme form is stabilized by pyridoxal 5'-phosphate. A new sedimentation equilibrium analytical procedure shows the dissociation of the second alpha subunit to be negatively cooperative. The analytical procedure calculates theoretical error profiles with assumed values of the dissociation constant, k, and a cooperativity parameter until a match is made between one of the theoretical profiles and that computed from experimental data. The latter profile is calculated with an experimentally determined k and assumed values of the cooperativity parameter.
authors.affiliation: New Ideas Company, Rockville, Maryland 20852, USA.
authors.forename: D B
authors.initials: DB
authors.lastname: Millar
mesh_terms: D003067:Coenzymes / Q000378:metabolism*; D004795:Enzyme Stability; D006146:Guanidines / Q000378:metabolism; D020035:Holoenzymes / Q000378:metabolism; D017879:Isothiocyanates / Q000378:metabolism; D007700:Kinetics; D011732:Pyridoxal Phosphate / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000201:enzymology; D013223:Statistics as Topic; D013816:Thermodynamics; D014367:Tryptophan Synthase / Q000378:metabolism*; D014461:Ultracentrifugation
chemical_list: D003067:Coenzymes; D006146:Guanidines; D020035:Holoenzymes; D017879:Isothiocyanates; C054435:guanidine isothiocyanate; D011732:Pyridoxal Phosphate; D014367:Tryptophan Synthase