Purification and Properties of Rat Liver Tryptophan Oxygenase

Abstract

Abstract Tryptophan oxygenase has been purified from livers of glucocorticoid and l-tryptophan-treated rats. Homogeneity of the enzyme was established by polyacrylamide electrophoresis, sedimentation experiments, and immunodiffusion. Amino acid analyses reveal 6 residues of cysteine per enzyme molecule. Analyses for heme content indicate 2 moles of heme per mole of enzyme. The sedimentation coefficient of the enzyme is 7.36 S. High speed equilibrium sedimentation experiments yield a molecular weight of 167,000. The optical spectra of the ferrienzyme as well as of the chemically reduced enzyme in the presence and absence of l-tryptophan are shown. The subunit structure of the enzyme was investigated by equilibrium sedimentation and electrophoresis at pH ≥12 and by electrophoresis in sodium dodecyl sulfate at pH 7.0. These studies indicate that hepatic tryptophan oxygenase is a tetramer composed of two pairs of identical subunits of equivalent mass (α2β2), the quaternary structure of which is stabilized exclusively by noncovalent interactions.