A new tool for quantification of membrane protein partitioning between different cell membranes.

The aqueous two-phase partition system (ATPS) is a method widely used to separate and purify plant and animal membranes carrying bound proteins. However, a common problem of this separation is a mutual contamination of obtained phases. Such contamination adversely affects the accuracy of values of the protein of interest partition between particular membranes when determined by direct measurement. In order to overcome this problem, we have developed a fairly simple mathematical algorithm and found formulas designed to quantify correctly the distribution of the protein of interest between two different membranes. This new tool makes it possible to determine the bias-adjusted ratio of protein distribution between the membranes, regardless of the efficiency of membrane separation in a two-phase system. By means of this algorithm, not only current, but also a number of previously published ATPS-based experiments were (re)analyzed and quantified. The quantitative results of this large-scale analysis of the subcellular localization of various membrane proteins from Arabidopsis, potato, melon, and corn including cytokinin and ethylene receptors, ABCG14 cytokinin transporters, LRR receptor-like protein kinases, and BAK1 co-receptors are presented and discussed here.