Impact of arginine addition on protein concentration via ultrafiltration

In this study, we examined the effects of arginine (L-ArgHCl) on ultrafiltration performance, a process with practical significance for not only research but also pharmaceutical applications. Specifically, we assessed the yield and filtration rate of ultrafiltration using rabbit and goat polyclonal antibodies (neutral to basic isoelectric points) as well as model proteins, BSA (acidic) and lysozyme (basic). When a 1 mg/mL protein solution was concentrated approximately 10-fold using a standard commercially available centrifugal ultrafiltration device, the addition of L-ArgHCl significantly improved yield at near-neutral buffer pH. The observed order of improvement was: 20 mM L-ArgHCl >100 mM L-ArgHCl ≈0.5 M NaCl > no addition. A similar trend was observed with BSA, whereas lysozyme achieved slightly higher yields at 100 mM L-ArgHCl. In a 40-fold concentration of rabbit polyclonal antibody from 1 mg/mL, 20 mM L-ArgHCl enhanced yield at pH 6 and 7, but had minimal or no effect at pH 7.5. Notably, at pH 8, high yields were achieved without arginine. L-ArgHCl also accelerated the concentration rate at all pH levels, with greater enhancements observed at higher arginine concentrations. These findings suggest that L-ArgHCl mitigates protein precipitation and solubility loss by reducing protein-protein interactions and nonspecific binding to the ultrafiltration membrane. At pH 8, the increased surface charge of the antibody reduced hydrophobicity, further improving solubility. In summary, the addition of L-ArgHCl, particularly near pH 7, effectively enhanced ultrafiltration performance. This provides a practical strategy for improving protein concentration processes.