Studies on the association of the α and β2 subunits of the tryptophan synthase of Bacillus subtilis

Studies using Sephadex gel filtration indicated that the α and β2 components of the Bacillus subtilis tryptophan synthase associate to form complexes under the appropriate conditions of buffer, pH, and temperature. Monovalent cations, glycerol, and the cofactor, pyridoxal-5′-phosphate, were required to maintain an active β2 component, and in turn, affected the association of the α and β2 components. Under conditions that stabilized the individual components during their purification, the affinity of the subunits for each other was weak. Under the same buffer conditions, but at the higher pH of 7.8 at which the enzymatic activities are assayed, the individual components readily associated. The substrate serine appeared to affect complex formation but there was no effect from the indole moiety. When the temperature was raised from 4 to 22–25 °C, complex formation was observed at both pH 6.6 and 7.8. The results of these experiments are consistent with the formation of αβ2 and α2β2 species as the associated tryptophan synthase complexes of B. subtilis.