Sodium carbonate versus borate buffer for lactase quenching, laboratory work.

A laboratory exercise for undergraduate advanced students of enzymology and biocatalysis is presented. Since enzyme assays can be quenched or continuous, this experiment compares the performance of two quenching agents for lactase, in a continuous setup. Enzymatic activity of β-galactosidase (Aspergillus oryzae) was determined based on the release of 4-nitrophenol from 4-nitrophenyl β-D-galactopyranoside using a microplate reader. Sodium carbonate and borate buffer were tested as quenching agents, and experimental control was the unstopped assay. Based on released 4-nitrophenol, enzyme activity, and rate constant k, the students could assess the performance of each termination agent. The experiment promotes disciplinary and transversal competencies, including research-based learning, critical thinking, and introduce the students to high-throughput techniques that are common in the research and development environment.