Differential effects of anionic surfactants on activities of GDH, LDH, and MDH

We systematically investigated, under stringent control environments, the effects of surfactants on enzymes in dilute solutions. We elucidated how anionic surfactants of various hydrophilicities affected the activities of three metabolically important enzymes - l-glutamate dehydrogenase (GDH), l-lactate dehydrogenase (LDH), and l-malate dehydrogenase (MDH) - of different molecular masses at a pH range important to body functions (6.5-7.4). We also investigated the time course of the surfactant concentration-dependent effects on LDH. As “standards” for comparison with results obtained using the anionic surfactants, we conducted similar studies with the well characterized non-ionic surfactant, Triton X-100. Activity of enzyme protein of larger molecular mass (GDH) in solution showed less variation compared to those with smaller molecular masses (LDH and MDH), with changes in pH, hydrophilicity, and surfactant concentration. For LDH and MDH, relative activities could change tremendously with 1 ppm difference in surfactant concentrations. All three enzymes were more active in hydrophilic than in hydrophobic surfactants. LDH activity also showed time-dependent decreases with different surfactant concentrations. These results suggest that, for data to be comprehensive, surfactant effects should be investigated with a wide range of concentrations and with time as a variable.