Rapid purification and characterization of cystine lyase b from broccoli inflorescence

We found three isoforms (a, b, and c) of cystine lyase in broccoli (Brassic a oleracea var. italica) inflorescence tissues. Cystine lyase b, the most a bundant isoform, was rapidly purified to homogeneity. The native enzyme had a M-r. of 160,000 and composed of four identical subunits with a M-r of 40 ,000. Thiocysteine and pyruvate were confirmed as reaction products. The pu rified cystine lyase b utilized L-cystine and S-alkyl L-cysteine sulfoxide as substrates. Other properties of cystine lyase b were almost similar to t hose of the isoform a as reported previously. Cystine lyase a and b were lo calized in cytosolic and/or vacuole fraction. A high activity of cystine ly ase was detected in some Allium species in addition to Cruciferae plants. ( C) 1999 Elsevier Science Ltd. All rights reserved.