The analysis of picomole amounts of L(+)- and D(-)-lactic acid in samples of dental plaque using bacterial luciferase.

L(+)-Lactic acid (5 pmol) and D(-)-lactic acid (20 pmol) were assayed by coupling the generation of NADH with the use of bacterial luciferase. The binding of NADH to L(+)-lactic dehydrogenase made it necessary to denature the protein so that the assay with bacterial luciferase was effective. The coupled luciferase assay of L(+)-lactic acid was 400 times more sensitive than the fluorometric assay. The luciferase coupled assay was used to analyze the L(+)- and D(-)-lactic acid contents of small samples of dental plaque.