SEDIMENTATION EQUILIBRIUM OF PAUCIDISPERSE SYSTEMS . SUBUNIT STRUCTURE OF COMPLEMENTED BETA-GALACTOSIDASE

Complemented β-galactosidase (of the ω-type) has been studied by equilibrium ultracentrifugation following dissociation with 6 m-guanidine-HCl. By proper choice of experimental conditions, two distinct polypeptide chains could be resolved, their respective molecular weights determined and their stoichiometry in the parent molecule assigned. The experimental techniques included modification of existing methods for measuring absolute concentrations with interference optics, based on the analysis of fringe diagrams recorded with both monochromatic and white light. Control experiments with a mixture of well-characterized proteins, constructed to approximate the results obtained for complemented β-galactosidase, confirmed the general validity of the methods described. The complemented enzyme was found to be composed of two distinct species of polypeptide chains of molecular weights 4 × 104 and 11 × 104, occurring in equimolar quantities. © 1969.