Planta Med 2008; 74(1): 73-79
DOI: 10.1055/s-2007-993777
Natural Product Chemistry
Original Paper
© Georg Thieme Verlag KG Stuttgart · New York

Unusual Cystine Lyase Activity of the Enzyme Alliinase: Direct Formation of Polysulphides

Michael Keusgen1
  • 1Institut für Pharmazeutische Chemie, Philipps-Universität Marburg, Marburg, Germany
Further Information

Publication History

Received: August 15, 2007 Revised: November 20, 2007

Accepted: November 26, 2007

Publication Date:
17 January 2008 (online)

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Abstract

Garlic (Allium sativum L.) and related species are highly estimated as foods, spices, and herbal remedies in many parts of the world. Sulphur-containing flavour compounds like allicin (allyl 2-propenethiosulphinate) are responsible for the smell and taste of freshly crunched garlic. These substances are formed by the action of alliinase (EC 4.4.1.4) on cysteine sulphoxides, e. g., alliin [S-(+)-allyl-L-cysteine sulphoxide]. Additionally, alliinase catalyses the C-S lysis of cystine in the manner of a cystine lyase. Ammonium, pyruvate and elementary sulphur but not cysteine could be detected as reaction products. The ratios between cystine, ammonium and pyruvate are 1 : 1.9 : 1.9 suggesting a new type of reaction mechanism. Thiocysteine and disulphine were assumed as intermediates. The pH optimum of the cystine lyase activity was found at pH 7.5 and the temperature optimum was at 44 °C. The KM value for the homogeneous enzyme was at 2.65 mM and Vmax was at 4.12 nkat/mg using cystine as substrate. Moreover, parallel incubation of cystine and alliin gave mainly allyl (poly)sulphides as reaction products instead of allicin. These substances had not been observed as direct enzymatic products until now. Thus, the significance of alliinase and its enzymatic products has to be newly considered in terms of ecological, pharmacological, and biochemical aspects.

References

Prof. Dr. Michael Keusgen

Institut für Pharmazeutische Chemie

Philipps Universität Marburg

Marbacher Weg 6

35032 Marburg

Germany

Phone: +49-6421-28-25809

Fax: +49-6421-28-26652

Email: Keusgen@staff.uni-marburg.de