L-Lactate Oxidase Systems of Microorganisms

Lactic acid (lactate) is among the most important natural α-hydroxy acids and is involved in a number of biological processes. Lactate is the terminal product of glucose metabolism in tissues under oxygen limitation, the major intercellular energy compound in human muscles and brain tissue, and a natural component of wines and other foodstuffs. Many microorganisms utilize L-lactate as a carbon and energy source, which provides for their survival and competitiveness with other species. Ability to utilize L-lactate is responsible for pathogenicity of some bacterial species, which is important in medical and pharmaceutical research. L-lactate-oxidizing enzymes are subdivided into soluble and insoluble ones. Soluble L-lactate oxidase systems include flavin-containing enzymes, which transfer electrons directly to oxygen (L-lactate oxidases and L-lactate monooxygenases). They are common among bacteria, yeasts, and fungi. Insoluble enzymes may contain both flavins and other components, including Fe-S clusters, which transfer electrons to the respiratory chain at the level of ubiquinone (coenzyme Q or menaquinone). In this case lactate oxidation is coupled to development of the transmembrane potential and ATP synthesis. These systems are present mostly in bacteria and algae. Investigation of the structure and organization of L-lactate utilization operons is an important aspect in investigation of L-lactate oxidase systems, since this approach may result in identification of new enzymes involved in lactate oxidation.