Colorimetric Coupled Enzyme Assay for Cystathionine β-Synthase

A colorimetric coupled enzyme assay for the determination of cystathionine β -synthase activity is described. The method exploits cystathionine γ -lyase as an ancillary enzyme capable of transforming cystathionine, produced by cystathionine β -synthase, into cysteine. The cysteine is then spectrophotometrically detected at 560 nm, after its specific complexation with ninhydrin. This method was used to detect cystathionine β -synthase in crude extracts, and for the kinetic characterization of the enzyme partially purified from bovine kidney. A rapid two-step protocol is described for the partial purification of cystathionine γ -lyase from bovine kidney, aimed at a suitable and stable ancillary enzyme preparation.