Figure 5.

Kinetic analysis of TSTD1 thiosulfate:thiol sulfurtransferase activity. TSTD1 sulfurtransferase activity was determined in the presence of 50 mm thiosulfate and varying concentrations of GSH (A), cysteine (C), or homocysteine (E). Dependence of the reaction velocity on thiosulfate (1–50 mm) was determined in the presence of 50 mm GSH (B), 50 mm cysteine (D), or 50 mm homocysteine (F), as described under “Experimental Procedures.” The data were fitted with the Michaelis–Menten or Hill equations and represent the mean ± S.D. (error bars) of three independent experiments performed in 300 mm HEPES, pH 7.4, 150 mm NaCl. Hill coefficients for the thiol acceptors GSH, cysteine, and homocysteine are 1.8 ± 0.2, 1.9 ± 0.1, and 2.0 ± 0.1, respectively.