Acetolactate synthase (ALS) is a key enzyme of pyruvate metabolism and produces acetolactate which can then be converted into the flavour compound, diacetyl. The ALS from Leuconostoc lactis NCW1 displays unusual kinetic properties and is expressed at low levels. Thus, the gene encoding ALS from Leuc, lactis NCW1 was cloned and over-expressed in Escherichia coli to facilitate a more detailed study of its functional properties. The recombinant enzyme, purified from E. coli, was active, and its specific activity was dependent on protein concentration, a phenomenon that was also observed in crude extracts of Leuc. lactis NCW1. Circular dichroism spectra of the purified enzyme revealed a loss of secondary structure of the enzyme upon dilution. In addition, the enzyme exhibited a number of multimeric forms on non-denaturing electrophoresis. The K-m for pyruvate and TPP decreased as the protein concentration increased. The evidence suggests that oligomerisation of enzyme subunits is enhanced at high protein concentrations and that the associated enzyme has greater specific activity than the individual monomers. The kinetic properties of this enzyme make its clone a candidate for the metabolic engineering of lactococcal strains for the increased production of diacetyl.