Lyase alliin

This enzyme [EC 4.4.1.6] catalyzes the pyridoxal-phos-phate-dependent hydrolysis of an 5-alkyl-L-cysteine to generate an alkyl thiol, ammonia, and pyruvate. The reaction is an a,/3-elimination. In yeast, the enzyme may be identical to cystathionine /3-lyase. See also Alliin Lyase... 

ALANINE RACEMASE S-ALKYLCYSTEINE LYASE ALLIIN LYASE... 

When garlic is cut and the parenchyma is destroyed, alliin is the major cysteine sulfoxide liberated. Alliin is acted upon by the enzyme allinase (alliin lyase) to produce allicin. Allicin [S-(2-... 

When garlic is mechanically disrupted, alliinase or alliin lyase (EC 4.4.1.4.) catalyzes the conversion of the cysteine sulfoxides to the biologically active diallyl thiosulfinates via sulfenic acid intermediates (Block, 1992). Alliinase is localized to a few vascular bundle sheath cells around the veins or phloem, whereas alliin and other cysteine sulfoxides are found in the clove mesophyll storage cells. This enzyme is approximately 10 times more abundant in the cloves than in the leaves and accounts for at least 10% of the total protein in the cloves (Ellmore and Feldberg, 1994). Alliinase is temperature and pH dependent optimal activity is between pH 5.0-10.0, but allinase can be irreversibly deactivated at pH 1.5-3.0 (Krest and Keusgen, 1999). 

Ellmore, G.S. and Feldberg, R.S. (1994) Alliin lyase localization in the bundle sheaths of the garlic clove (Allium sativum). Am. J. Bot. 81 89-94. 

The C-S lyase [alliin alkyl-sulfenate-lyase (EC 4.4.1.4), alliinase, alliin lyase, alkylcysteine sulfoxide lyase, cysteine sulfoxide lyase] is an enzyme responsible for the flavor production Ifom 5 -alk(en)yl-L-... 

Jansen, H., Muller, B., and Knohloch, K. 1989. Characterization of an alliin lyase preparation from garlic (Allium sativum). PlantaMed 55(5) 434-439. 

Nock, L.P. and Mazelis, M. 1987. The C-S lyases of higher plants Direct comparison of the physical properties of homogenous alliin lyase of garlic Allium sativum) and onion Allium cepa). Plant Physiol S5(4) 1079-1083. 

For the time being, a number of perplexing questions are still unsolved. For example - why are exclusively B-elimina-ting lyases, such as serine (threonine) dehydratase, alliin lyase etc., incapable to effect a replacement step (Michael addition) — what is the difference in dynamic topography (stereochemistry) between this enzyme subtype and the ambi-functional Q-lyases, displaying the same behaviour towards L-cycloserine or aminothiol inhibitors,etc. Further investl-ons are needed to shed light on these and other obscure aspects of the problem. 

Alliin, the major compound in Allium sativum and A. ursinum, is unstable in water extract.s. The enzyme alkykulphinate lyase (allinase = allinlyase) splits alliin to allidn, which it,self generates further sulphur-containing degradation or transformation products (e.g. ajoenes). 

The flavor precursors, 5 -alk(en)yl-L-cysteine sulfoxides, themselves do not have any specific flavor. However, when garlic or onion cells are damaged by cutting or crushing and the 5 -alk(en)yl-L-cysteine sulfoxides meet the C-S lyase (alliinase), they are converted into various volatile sulfuric compounds. Stoll and Seebeck (1951) first proposed the production of diallyl thiosulfinate (allicin) from the 5 -allyl-L-cysteine sulfoxide (alliin) by the C-S lyase. Through the reaction catalyzed by the C-S lyase, 5 -alk(en)yl-L-cysteine sulfoxides yield alk(en)yl sulfenic acid and aminoacrylic acid, the latter being spontaneously degraded... 

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