The bioemulsifier alasan: Role of protein in maintaining structure and activity

Alasan, the bioemulsifier of Acinetobacter radioresistens KA53, is a high-molecular-mass complex of polysaccharide and protein. Enrichment culture was used to isolate a bacterial strain that grew on alasan as the sole source of carbon and energy, causing the loss of the protein portion of alasan, as well as the emulsifying activity. The degradation was mediated by extracellular proteinases/alasanases. One of these enzymes, referred to as alasanase II, was purified to homogeneity. Alasanase II, as well as pronase, inactivated alasan, whereas a polysaccharide-degrading enzyme mixture, snail juice, had no effect on emulsifying activity. Deproteinization of alasan with phenol yielded a viscous polysaccharide with no emulsifying activity. Heating alasan to 50°C led to a 2.5-fold irreversible increase in viscosity with no change in emulsifying activity. Heating to 60°-90°C caused a drop in viscosity and a 5.8-fold increase in emulsifying activity. The deproteinized alasan showed no increase in emulsifying activity and only small changes in viscosity when heated.