[18] Zonal centrifugation. Enzyme purification and related techniques. Elsevier; 1971. pp. 168-204. [DOI: 10.1016/0076-6879(71)22020-6]

Zonal rotor centrifugation revisited: new horizons in sorting nanoparticles

Density gradient centrifugation is an effective method for the isolation and purification of small particles. Hollow rotors capable of hosting density gradients replace the need for centrifuge tubes and therefore allow separations at large scales. So far, zonal rotors have been used for biological separations ranging from the purification of whole cells down to serum proteins. We demonstrate that the high-resolution separation method opens up exciting perspectives apart from biology, namely in sorting mixtures of synthetic nanoparticles. Loading and unloading, while the rotor is spinning, avoids perturbations during acceleration and deceleration periods, and thus makes a vital contribution to sorting accuracy. Nowadays one can synthesize nanoscale particles in a wide variety of compositions and shapes. A prominent example for this are “colloidal molecules” or, generally speaking, defined assemblies of nanoparticles that can appear in varying aggregation numbers. Fractionation of such multimodal colloids plays an essential role with regard to their organization into hierarchical organized superstructures such as films, mesocrystals and metamaterials. Zonal rotor centrifugation was found to be a scalable method of getting “colloidal molecules” properly sorted. It allows access to pure fractions of particle monomers, dimers, and trimers, just as well as to fractions that are essentially rich in particle tetramers. Separations were evaluated by differential centrifugal sedimentation, which provides high-resolution size distributions of the collected nanoparticle fractions. The performance achieved in relation to resolution, zone widths, sorting efficiencies and recovery rates clearly demonstrate that zonal rotor centrifugation provides an excellent solution to the fractionation of nanoparticle mixtures.

Hollow bowl-shaped rotors allow for efficient fractionation of nanoparticle mixtures at large scale.

Major outer membrane proteins of Pasteurella haemolytica serovars 1-15: comparison of separation techniques and surface-exposed proteins on selected serovars

The Sarkosyl method of obtaining outer membrane proteins (OMPs) from Pasteurella haemolytica A1 was more efficient and less laborious than separating membranes by sucrose gradient centrifugation. More OMPs were recovered and major OMPs were present in greater concentrations in the Sarkosyl-derived preparations. Therefore, OMPs of P. haemolytica serovars 1-15 (serovars 3, 4, 10, and 15 being T biotypes and the remainder being A biotypes) were prepared by the Sarkosyl method and compared by SDS-PAGE. Serovars 1, 2, 5, 6, 7, 8, 11, and 12 which are A biovars had similar OMP profiles characterized by major OMPs of 30.5 and 43 kDa. Biovar T strains were characterized by doublet protein bands in the 26-28 kDa region and a major OMP in the 38-40 kDa range. Serovars 9, 13, and 14, which are also A biovars, had profiles similar, although not identical, to the T biovars. A 43 kDa protein was present in all serovars although concentration was greater in the A biovars. Surface-exposed proteins of P. haemolytica A1 determined by 125I-labeling of whole cells were 94, 84, 53.5, 49, 43, 41, 29.5, and 16 kDa. Iodine-labeling of serovars A2 and A6 which have similar OMP profiles by SDS-PAGE resulted in autoradiographs indistinguishable from A1. These studies expand our knowledge of P. haemolytica OMPs especially showing the utility of the Sarkosyl extraction procedure, variations in OMP profiles among some A biovar strains, and the similarities of OMP profiles and surface-labeled proteins among three of the most important serovars (1, 2, and 6).

Sedimentation characteristics of vesicles associated with insulin-sensitive intracellular glucose transporter from rat adipocytes

The sedimentation characteristics of vesicles associated with the insulin-sensitive intracellular glucose transporter from rat adipocytes were studied. The method used was sucrose density gradient centrifugation, which was carried out under non-equilibrium and equilibrium (isopycnic) conditions. The glucose transport activity was determined by the reconstitution method. As reported previously, the sedimentation velocity of the intracellular glucose-transport activity was considerably slower than that of the counterpart in the plasma membrane. It was found, however, that the specific gravity of the slow-sedimenting glucose-transport activity was almost identical to that of the activity in the plasma membrane (d = 1.118-1.122). It is concluded that the intracellular glucose transport activity is associated not with low-density microsomal vesicles, but with unidentified slow-sedimenting vesicles that have a specific gravity similar to that of the plasma membrane.

Collagenase: localization in polymorphonuclear leukocyte granules in the rabbit

Polymorphonuclear leukocyte granules were submitted to zonal fractionation through a discontinuous sucrose gradient. Azurophilic and specific granules were enzymatically characterized by peroxidase and alkaline phosphatase activity, respectively. The enzymes formed modal distributions like those reported by others. Collagenase activity was consistently associated with the specific granules containing alkaline phosphatase.