How do ultracentrifuges help purify proteins and viruses?

Ultracentrifuges are essential tools for purifying proteins and viruses because they generate the high centrifugal fields—often exceeding 300,000g—necessary to sediment such small, submicroscopic particles. By spinning at speeds typically above 20,000 revolutions per minute within an evacuated chamber, these machines eliminate air resistance, which prevents heat buildup and convection currents that would otherwise disturb the sedimentation process.12

Purification is achieved through several methods:

• Sedimentation: Particles are separated based on differences in weight and size as they move through a solution under high centrifugal force.32
• Density-Gradient Centrifugation: A radial density gradient is established using nonreactive molecules like sucrose. When a mixture is centrifuged, substances collect in thin layers at specific radii corresponding to their unique particle densities.1
• Continuous-Flow: Vacuum-type tubular centrifuges allow for the continuous processing of biological materials, which is particularly effective for large-scale purification needs.1

These techniques allow researchers to isolate specific biological components from complex mixtures, facilitating the study of molecular weights and the production of purified materials for medical and biochemical applications.13