Cystathionine β-lyase from Echinochloa colonum tissue culture

Cystathionine beta-lyase (EC 4.4. 1.8), the second enzyme unique to methionine biosynthesis, catalyses the alpha,beta-elimination of cystathionine to yield homocysteine, pyruvate, and ammonia. The enzyme was purified to electrophoretic homogeneity from cell suspension cultures of Echinochloa colonum. Purification was achieved following ammonium sulphate fractionation and ion-exchange, hydrophobic-interaction, size-exclusion, and dye-affinity chromatography. The specific activity of cystathionine beta-lyase in the final extract was 11 900 nmol min(-1) mg(-1) (protein). This represented a 5400-fold purification and a recovery of 50%. The substrate specificity was limited to cystathionine and djenkolate, and the beta,gamma-unsaturated amino acid aminoethoxyvinylglycine was a reversible competitive inhibitor with an apparent inhibition constant of 23.4 mu M. The enzyme had a tetrameric quaternary structure with a subunit M-r of 43 k. Isoenzyme analysis of cystathionine beta-lyase was performed by ion exchange chromatography. In extracts of E. colomun cell suspension cultures, leaves, and roots a single form of cystathionine beta-lyase was eluted from the ion exchange column between 180 and 190 mM KCI. (C) 1997 Elsevier Science Ltd.