Stabilization of Alliinase from Garlic by Osmolytes and the Mannose-Specific Lectin ASAI

Objectives: Alliinase is a pyridoxal-5'-phosphate (PLP)-dependent enzyme responsible for the production of diallyl thiosulfinate (allicin), the biologically active component of garlic, from alliin. The use of allicin for treatment of various diseases has been proposed but it is very unstable in the blood stream. This difficulty can be overcome by administration of alliin, together with a conjugate of alliinase directed towards the target cells. This, in turn requires a stable and active form of the enzyme. In this study we evaluate the stability of alliinase itself, in the presence and absence of osmolytes, as well as that of its catalytically active complex with a mannose-specific lectin, ASAI (Allium sativum agglutinin I), also presents in garlic. Methods: Alliinase, and ASAI were both purified from garlic cloves. Thermal stability of alliinase itself, and of its complexes with PLP and ASAI, in the presence and absence of osmolytes, was analyzed by monitoring enzymic activity, and using DSC (differential scanning calorimetry). Key findings: PLP exerts only a minor influence on alliinase structure and stablity. But both osmolytes and ASAI stabilize the enzyme considerably. Conclusions: The principle finding is that ASAI greatly stabilizes alliinase. Thus, the lectin-enzyme complex, which can be lyophilized and stored until used, provides an effective formulation of alliinase for generation of allicin from alliin in vivo.