An extensive proteomic approach relies on the possibility to visualize and analyze various types of proteins, including membrane proteins, which are rarely detectable on two-dimensional electrophoresis gels. In this study, different methods were employed for the enrichment of membrane proteins from Chlorobium tepidum prior to analysis with two-dimensional electrophoresis (2-DE). Isolated membranes were solubilized with Triton X-100 and from the supernatant we identified 58 unique proteins. The use of ionic sodium dodecyl sulfate (SDS) for protein solubilization, combined with acetone precipitation, resulted in an improved 2-DE pattern and the total number of the identified proteins was increased to 117. The use of acetone for protein precipitation improved the results by extracting compounds potentially deleterious to the resolution of 2-DE. However, the additional proteins detected by the use of SDS are in the majority more difficult to solubilize than less hydrophobic proteins. Further our attempts for selective extraction of the outer membrane proteins using the acid glycine method allowed the identification of 37 proteins of which 14 were predicted to have a signal sequence indicating their localization in the periplasmic space or in the outer membrane.

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The protein and lipid composition of a vitellin isolated from eggs of Sparus aurata were characterized by SDS PAGE, N-terminal sequence analysis and lipid analysis by thin layer chromatography and gas chromatography. The lipoprotein complex contains proteins with apparent molecular weights of 69, 59, 23, 21 and 12 kDa and were characterized as vitellinogenin fragments by N-terminal sequencing. Lipid extraction and analysis indicate an association of cholesterol and phospholipids with the protein subunits. The phospholipids contain fatty acids with 14, 16 and 18 carbon atoms as determined by GC/MS.

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