Partition coefficient of luciferase from photobacteria in PEG/salt two aqueous phase system

The relationship between the logarithmic partition coefficient (K) of luciferase of photobacteria and PEG MW in the PEG/salt two aqueous phase system was shown to be a linear function. The hydrophilic PEG of lower MW facilitated the partition of luciferase into the top PEG-riching phase and gave a higher K value, while PEG of higher MW, its hydrophobic characteristic, made more enzyme partition into the bottom salt-riching phase and lower K value was obtained. In the PEG/trivalent salt system, such as phosphate and citrate, there was a turning-point on the linear relation between the log K and the PEG MW, but which never appeared if a divalent salt such as sulfate, succinate or tartrate was used in the system. When the system was composed of homogeneous PEG and ammonium sulfate, the K value was increased with the increment of the salt concentration, but after the salt concentration had reached at certain level, the K value was uninfluenced. When two kinds of PEG with different MW were used in this system a minimal K value appeared at certain concentration of ammonium sulfate, and the K value was raised when the salt concentration was either increased or decreased. Neither the proportion of the two kinds of PEG nor their total concentration used in the system showed any effect on the above patterns, although the K value may give some corresponding changes. (ABSTRACT TRUNCATED AT 250 WORDS)