Fig. 4

(A) Pre-column derivatization of L-homocysteine with DTNB. (B) Chromatograms of components of the control (upper) as well as enzymatic (lower) reaction mixtures. The reaction mixture contained 25 mM Tris-HCl pH 8.0; 100 mM NaCl; 10 mM O-acetyl-L-homoserine; 0.1 mM Na₂S; and 0.2 mM PLP. The reaction was started by the addition of 10 nM pure enzyme. The control mixture contained all ingredients except the substrate O-acetyl-L-homoserine. (C) Mass spectrometry (MS) analysis of the enzymatic reaction (r.t 7.8 min). m/z: [HCT-TNB + H]⁺ 333.0.