RESUMEN
This work investigated the partitioning of (beta)-galactosidase from "Kluyveromyces fragilis" in aqueous two-phase systems (ATPS) by bioaffinity. PEG 4000 was chemically activated with thresyl chloride, and the biospecific ligand p-aminophenyl 1-thio-(beta)-D-galactopyranoside (APGP) was attached to the activated PEG 4000. A new two-step method for extraction and purification of the enzyme (beta)-galactosidase from "Kluyveromyces fragilis" was developed. In the first step, a system composed of 6(per cent) PEG 4000-APGP and 8(per cent) dextran 505 was used, where (beta)-galactosidase was strongly partitioned to the top phase (K = 2.330). In the second step, a system formed of 13(per cent) Peg-APGP and 9(per cent) phosphate salt was used to revert the value of the partition coefficient of (beta)-galactosidase (K = 2.0E-5) in order to provide the purification and recovery of 39(per cent) of the enzyme in the bottom salt-rich phase