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A new approach to affinity purification is described which combines affinity binding with ultrafiltration separation. In this approach, a macromolecular ligand is retained on one side of a membrane and is allowed to interact with a crude extract. Material specifically binding to the ligand forms a high-molecular-weight complex whereas all other material is washed out through the membrane pores. On addition of free ligands or other dissociation media the complexes dissociate and the formerly bound material is liberated, passed through the membrane and collected in a purified state. This paper describes the purification of concanavalin A from a crude extract of Canavalia ensiformis using the surface structures of heat-killed yeast cells (Saccharomyces cerevisiae as macromolecular ligands. A high capacity for concanavalin A was demonstrated. The yield over the total process was ca. 70% and the product was homogenous when analyzed by SDS–polyacrylamide gel electrophoresis.

Alginate entrapped Pseudomonas denitrificans have been compared with cells confined in the outer space of a hollow-fiber membrane unit with respect to continuous denitrification of water. The hollow-fiber unit had a higher productivity as well as a stability similar to that of the alginate unit. A reduction of cell-leakage in the eluate was found in the hollow-fiber unit. The nitrogen gas produced could be removed by circulating the cell containing fluid over a hydrophobic membrane.

Affinity chromatography has over the last ten years developed from being a research instrument to becoming a routinely used method. A leading theme during these developments ahs been to use affinity sorbents, which from a chemical point of view, were well-defined and offered few possibilities for unspecific interactions. However, some ligands may be too complicated or too expensive tc synthesize in order to be used as affinity ligands. Therefore, a recent development in affinity chromatography has dealt with the use of immobilized whole cells as affinity supports and surface structures on these immobilized cells have been used as ligands. Recently, cells cross linked by glutaraldehyde and mixed with Sephadex G-25 have been used in lectin purification (1). The use of cells adsorbed to ion-exchangers as affinity systems has also been described (2), but serious leakage of cells from the support took place during the affinity chromatographic procedure.

A novel immunochemical method for the quantitation of bacterial cells is described. The method, which is based on separation of bound from free reactants in aqueous two-phase systems has been studied both as direct and competitive binding assays, with a system consisting of intact cells of Staphylococcus aureus and human immunoglobulin G molecules. To achieve high resolution, one of the reactants was modified so that the two reactants, the bacterial cells and the immunoglobulin molecules, occurred in different phases of the phase system. When binding takes place, the partition of one of the reactants is changed. The degree of change is then correlated to the amount of reactant present. Using this method, cell numbers in the region 10 5 –10 7 can be quantified. An assay takes 40–90 min.