Thermal stability of high concentration lysozyme across varying pH: A Fourier Transform Infrared study

AIM: The current work is aimed at understanding the effect of pH on the thermal stability of hen egg white lysozyme (HEWL) at high concentration (200 mg/mL). MATERIALS AND METHODS: Fourier Transform Infrared (FTIR) Spectroscopy with modified hardware and software to overcome some of the traditional challenges like water subtraction, sample evaporation, proper purging etc., are used in this study. RESULTS: HEWL was subjected to thermal stress at pH 3.0-7.0 between 25°C and 95°C and monitored by FTIR spectroscopy. Calculated T(m) values showed that the enzyme exhibited maximum thermal stability at pH 5.0. Second derivative plots constructed in the amide I region suggested that at pH 5.0 the enzyme possessed higher amount of α-helix and lower amount of aggregates, when compared to other pHs. CONCLUSIONS: Considering the fact that HEWL has attractive applications in various industries and being processed under different experimental conditions including high temperatures, our work is able to reveal the reason behind the pH dependent thermal stability of HEWL at high concentration, when subjected to heat denaturation. In future, studies should aim at using various excipients that may help to increase the stability and activity of the enzyme at this high concentration.