PARTITIONING OF PROTEINS AND THYLAKOID MEMBRANE-VESICLES IN AQUEOUS 2-PHASE SYSTEMS WITH HYDROPHOBICALLY-MODIFIED DEXTRAN

Dextrans were modified with hydrophobic groups, i.e. benzoyl and valer yl groups. Benzoyl dextran and valeryl dextran form aqueous two-phase systems with poly(ethylene glycol) (PEG) as well as with dextran. Two- phase systems are also formed between two valeryl dextrans with differ ent degrees of substitution as well as between benzoyl dextran and val eryl dextran. Phase diagrams for aqueous two-phase systems composed of PEG-valeryl dextran, dextran-valeryl dextran, valeryl dextran-valeryl dextran and valeryl dextran-benzoyl dextran have been determined. The effects of these hydrophobic groups on the partitioning of amino acid s, proteins and membrane vesicles in aqueous two-phase systems have be en studied. In a PEG 8000-dextran T500 aqueous two-phase system contai ning only phosphate buffer beta-galactosidase was partitioned mostly t o the top phase. However, by introducing a small amount of benzoyl gro ups (degree of substitution 0.054) or valeryl groups (degree of substi tution 0.12) in the lower phase, the partition coefficient of this enz yme could be decreased by more than 100 times. A similar, but weaker, effect on partitioning was observed for bovine serum albumin, lysozyme , lipase and beta-lactoglobulin. The partitioning of thylakoid membran e vesicles was strongly affected by the hydrophobic groups on dextran. The membrane vesicles were partitioned toward the phase containing th e hydrophobic groups.