The C-S Lyases of Higher Plants

Abstract

Cystine lyase degrades L-cystine by a al-elimination to form cysteine persulide, pyruvate, and ammonia. This enzyme is common in Brassica sp. and has been purified to homogeneity from extracts of broccoli (Brassica okeracea var botrytis) buds. Two isozymes were separated on DEAE-Fractogel columns and the first peak, cystine lyase I further purified to homogeneity. The purified enzyme had a narrow range of substrate specificity with L-cystine and S-alkyl-L-cysteine sulfoxides being the primary substrates. The K,. for L-cystine was 1.9 millimolar and for S-ethyl-L-cysteine sulfoxide was 15.6 millimolar, suggesting that L-cystine would be prefeffed in vivo. Using gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis the molecular weight of the holoenzyme was estimated as 152,000 composed of subunits of approximately 49,000. This strongly suggests the native enzyme is a trimer. The presence of carbohydrate in the native enzyme was detected at the level of 5.8% on a weight basis. Except for the ability to utilize Lcystine as a substrate there are many similarities between cystine lyase I and the alliin lyase of onion (Allium cepa).This enzyme has been purified to homogeneity from garlic (8,14) and onion (17) and found in a number of Brassica sp. (10). The garlic and onion enzymes are specific for S-alkyl-L-cysteine sulfoxides, however the Brassica preparations studied to date (1,6,11,12) also can cleave L-cystine according to reaction 2: S -s H2C +

A New Member of Plant CS-lyases

“…Only two peaks, in the HPLC chromatogram of the two digests, displayed a different elution pattern. This supports that the two 43-kDa polypeptides are two closely related isoforms, as suggested previously (5,25). Two peaks that appeared in the chromatograms of both digests (fraction 63 and 75, Fig.…”

“…The purification of a plant cystine lyase is not novel (1,16,25); however, the identification of a plant-derived nucleic acid sequence that encodes a cystine lyase, CORI3, certainly is. The isolation of BOCL3 and its corresponding cDNA clone by classical biochemical methods proved essential for the identification of the true function of the protein encoded by CORI3.…”

Engineering Saccharomyces cerevisiae To Release 3-Mercaptohexan-1-ol during Fermentation through Overexpression of an S. cerevisiae Gene, STR3 , for Improvement of Wine Aroma

“…The latter substrate, together with S-methyl-L-cysteine sulfoxide, occurs in high concentrations in Brassica and Allium vegetables. Characteristic flavors of these vegetables are partly derived through enzymatic degradation of these amino acids by CS lyases when their tissue is disrupted (11).…”

Purification and Characterization of Cystine Lyase a from Broccoli Inflorescence

“…1) This enzyme has been found in several Cruciferae 1) and partially purified from cabbage 2 ) and turnip.3) One of the 1soforms of cystine lyase has been purified to homogeneity from broccoli. 4 ) Similar enzymes were purified from onion, 5) garlic,6) and leek,7) all in the genus Alliwn, and from A cacia/ilrnesiana, 8) in the family Fabaceae. In most earlier studies of cystine lyase, the enzyme was assayed in terms of the amount of pyruvate formed, without direct proof that thiocysteine was actually formed.…”