The Role of Caprylate Ligand Ion on the Stabilization of Human Serum Albumin

Sodium caprylate was added to a pharmaceutical-grade human serum albumin (HSA) to stabilize the product. In this study we have aimed to establish how caprylate ligand protects HSA from thermal degradation. The fatty acid stabilizer was first removed from commercial HSA by charcoal treatment. Cleaned HSA was made to 10% w/v in pH 7.4 buffered solutions and doped with sodium caprylate in serial concentrations up to 0.16 mmol/g-protein. These solutions as well as a commercial HSA, human serum, and enriched-albumin fraction were subjected to differential scanning calorimetry (DSC) within the temperature range of 37–90°C at a 5.0°C/min scanning rate. The globular size of the cleaned HSA solutions was measured by dynamic light scattering. The denaturing temperatures for albumin with sodium caprylate and a commercial one were significantly higher than for albumin only. It was found that the protein globules of cleaned HSA were not as stable as that of the native one due to aggregation, and the caprylate ion may reduce the aggregation by enlarging the globules’ electrical double layer. A rational approximation of the Lumry-Eyring protein denaturation model was used to treat DSC denaturing endotherms. The system turned from irreversible dominant Scheme: to reversible dominant Scheme: with the increase in caprylate concentration from null to ~0.08 mmol/g-protein. It was postulated that the caprylate ligand may decrease the rate of reversible unfolding as it binds to the IIIA domain which is prone to reversible unfolding/refolding and causes further difficulty for irreversible denaturation which, in turn, HSA can be stabilized.KEY WORDS: differential scanning calorimetry, human serum albumin, Lumry-Eyring model, protein denaturation, sodium caprylate     

Selection and identification of anaerobic lactobacilli producing inhibitory compounds against vaginal pathogens

Two strains of Lactobacillus crispatus (15L08 and 21L07) and one strain of Lactobacillus jensenii (5L08) were selected from amongst 100 isolates from the vaginas of healthy premenopausal women for properties relevant to mucosal colonization and the production of H2O2 and/or bacteriocin-like compound. All three strains self-aggregated and adhered to vaginal epithelial cells, displacing well-known vaginal pathogens, such as Gardnerella vaginalis and Candida albicans. Lactobacillus crispatus 15L08 was characterized as a potential H2O2 producer. A high level of bacteriocin-like compound was synthesized by L. jensenii 5L08, with a bactericidal mode of action for G. vaginalis, C. albicans and Escherichia coli. However, H2O2-dependent activity alone was not sufficient to inhibit the growth of C. albicans. Simultaneous actions of H2O2 and bacteriocin-like compound produced by lactobacilli may be important for antagonizing pathogenic bacteria. These strains of lactobacilli may be excellent candidates for eventual use as probiotics to restore the normal microbial communities in the vaginal ecosystem.