Characteristics of lipids in microdomains extracted by different methods from vacuolar membranes

Abstract

The presence of lipid-protein microdomains in biological membranes is considered proven in biological literature. The content of lipids and proteins in the microdomains depends on the membrane’s nature, as well as on the technique used for isolation of the membrane fractions. In the case of detergent technique (DT), the nativity of the microdomains (called rafts) is questioned. In this connection, in our studies isolation of tonoplast fractions was performed using not only by the well-known detergent technique but also by a milder detergent-free technique (DFT). The microdomains were identified in the fractions, and the comparative analysis of lipid content of tonoplast microdomains in the fractions isolated by the two techniques was conducted. It was demonstrated that microdomains isolated from tonoplast by DFT substantially differ in their lipid content from those isolated with the use of Triton X-100. This means that such microdomains cannot be qualified as rafts, despite the fact that they are located in the same opalescence zone of the sucrose density gradient, as the microdomains obtained from the fraction isolated with the use of Triton X-100 have a higher (than in the initial tonoplast) content of sterols and their esters. As far as the microdomains identified in the fraction obtained by DFT are concerned, we have revealed an unusual content of polar lipids, half of which is represented by the lipids (phosphatidylethanolamine, phosphatidic acid and monogalactosyldiglyceride) capable (under definite conditions and due to lipid polymorphism) of the formation of hexagonal structures, which are believed to participate in transport of water-soluble metabolites.