Effect of Sulphydryl Group Reagents on Tryptophanase Activity

Abstract

BOTH Gunsalus et al. ¹ and Wada et al. ² have reported that the presence of glutathione is advantageous during the assay of tryptophanase preparations. Wada et al. have also reported studies on the inhibition of tryptophanase by a number of SH-group reagents, and have suggested that the group is involved in the linkage between apoenzyme and substrate³. When we compare results which we have obtained at intervals since 1942, there is much agreement between us, but divergences, which may or may not be significant, do exist. Evans, Handley and Happold⁴ reported a 12–20 per cent reduction of activity in washed cell preparation with sodium iodoacetate in a final concentration of M/33, and in later work with cell-free preparations activities were reduced by 20–25 per cent at concentrations of 5 × 10⁻³ M. At lower concentrations 5 × 10⁻⁵ and 10⁻⁶ M there has been no inactivation or even from time to time an apparent increase in the activity of the preparations. Further studies on, inhibition were reported by Dawes and Happold⁵. Such preparations of tryptophanase are not necessarily free from other enzymes associated with pyridoxal phosphate-linked enzyme systems nor from the system which produced pyridoxal phosphate from pyridoxamine phosphate which Beechey and Happold described as a transaminase and which we now know contains a pyridoxamine phosphate oxidase similar to that found by Pogell in rabbit liver preparations; these divergences may be significant. During work in these laboratories on the purification of tryptophanase, the inhibition of activity by the SH-group alkylating reagent chloroacetophenone, and the reversal of SH-group inactivation, have been studied.