Cysteine sulphoxides, amino acids and alliinase activity of Allium nigrum

Allium nigrum L. belongs to the subgenus Melanocrommyum of the genus Allium. This subgenus is widely distributed in Southwest and Central Asia. However, A. nigrum is a typical plant of east Mediterranean islands. Many species of this subgenus were traditionally used. A. nigrum is reported to be active against helminthiasis. Typical for the genus Allium is a rather high content of cysteine sulphoxides. Most abundant is the cysteine sulphoxide methiin (1). Recently, an unusual cysteine sulphoxide containing a pyrrole ring system (2) could be reported [1]. Both compounds were also present in A. nigrum. Amino acid derivatives were analysed as corresponding o-phthaldialdehyde derivatives by means of HPLC-MS/MS. For methiin (1) and the pyrrole derivative (2), average concentrations of 0.04% and 0.01%, respectively, were found (concentrations related to the fresh weight of bulbs). If these cysteine sulphoxides would be incubated with the enzyme alliinase, a number of thiosulphinates can be expected. Enzymatic incubations were also performed for the low molecular weight extract of A. nigrum and resulting compounds were analyzed by HPLC-MS/MS. Interestingly, only the pyrrole derivative (3) could be detected. It is completely unclear in which manner methiin (1) reacts with the alliinase of A. nigrum. It can be supposed that this alliinase acts different from the well described alliinase of A. sativum (garlic).

Reference: [1] Jedelská, J. et al. (2008)J. Agric. Food Chem. 56:1465–70