Ligand‐Binding Studies on Heavy Riboflavin Synthase of Bacillus subtilis

Abstract
Heavy riboflavin synthase [of B. subtilis] is a complex enzyme consisting of 3 .alpha. subunits and .apprx. 60 .beta. subunits. Ligand-binding studies were performed with a variety of substrate and product analogs by analytical ultracentrifugation and by equilibrium dialysis. Nonlinear binding curves indicate the involvement of nonequivalent binding sites which could be assigned to the .alpha. and .beta. subunits by comparison with light riboflavin synthase (subunit composition .alpha.3) and with aggregates of isolated .beta. subunits. The .beta. subunit binding site shows a high degree of stereospecificity. Tightly binding ligands must have a ribityl side chain and a pyrimidine or pteridine moiety with polar substituents.