Anomalous salting-out behaviour of cyanogen bromide fragments of bovine serum albumin

The solubilities of bovine serum albumin and its two cyanogen bromide fragments comprising domain I and II+III of the protein in ammonium sulphate solution were studied at different pH and temperature and the salting-out parameters K_s and β were determined for the three proteins. The values of K_s and β obtained for the intact albumin at different pH were atypical of other globular proteins and were explained in terms of N-F transition and pH induced unfolding of the protein. The salting-out behaviour of the two fragments was, however, found to be significantly different from that of their parent molecule. In contrast to bovine serum albumin, the aqueous solubilities of the two fragments were highly dependent on temperature. Similarly, pH dependence of β for the two fragments was also different since it acquired a minimum value at about pH 4.0 as against its monotonic decrease with pH observed in intact albumin below pH 5.0. Anomalous salting-out behaviour of the two cyanogen bromide fragments has been attributed to the possible conformational changes that might occur during the course of their preparation under relatively harsher chemical conditions.