A mathematical model to predict the partitioning of peptides and peptide-modified proteins in aqueous two-phase systems.

A mathematical procedure was developed to predict the partition coefficients of the peptides AIIP, AWWP, AIIPAIIP and AWWPAWWP in poly(ethylene glycol) (PEG)/phosphate aqueous two-phase systems from amino acid hydrophobicities. In general, peptides containing tryptophan partition more into the PEG-enriched upper phase than analogous peptides containing isoleucine. Specifically, as the PEG concentration difference between the phases increased in a PEG/potassium phosphate aqueous two-phase system, the peptide AIIP was observed to have a partition coefficient ranging from 1.

Polyethylene glycol-potassium phosphate aqueous two-phase systems. Insertion of short peptide units into a protein and its effects on partitioning.

Two different tetrapeptides, AlaTrpTrpPro and AlaIleIlePro, were inserted near the C-terminus of the protein ZZT0. The Trp-rich peptide unit strongly increased both the partitioning of ZZT0 into the polyethylene glycol (PEG)-rich phase in a PEG-potassium phosphate aqueous two-phase system and its retention on PEG and propyl hydrophobic interaction chromatographic columns with potassium phosphate as eluent. Both the partitioning and the retention increased with increasing number of Trp-rich peptide units inserted into ZZT0.