The C-S lyases of higher plants: preparation and properties of homogeneous alliin lyase from garlic (Allium sativum)

Alliin lyase from garlic (Allium sativum) has been purified to homogeneity. The purification procedure involves the use of affinity chromatography on concanavalin A-Sepharose 4B. Addition of polyvinylpolypyrrolidone to the homogenizing medium greatly improves the specific activity of the extract. The enzyme is a glycoprotein as seen by its ability to bind to concanavalin A-Sepharose 4B and by its positive periodic acid-Schiff base stain. It has a carbohydrate content of 5.5%. Km values for this enzyme were estimated to be 5.7 mM for S-ethyl-L-cysteine sulfoxide and 3.3 mM for S-allyl-L-cysteine sulfoxide. The molecular weight of this garlic enzyme, as determined by gel filtration, was found to be 85,000; the molecule consists of two equal subunits of Mr 42,000. The amino acid content was found to be similar to that reported previously for onion alliin lyase, although there is twice as much tryptophan in the garlic alliin lyase as in the onion enzyme. By both chemical and spectral methods the enzyme was found to have two molecules of pyridoxal 5-phosphate per enzyme molecule, suggesting one per subunit. There are significant differences in the nature of these findings from those previously reported from this laboratory for the onion enzyme. Studies are in progress to compare further the alliin lyases from garlic and onion.