MS-based analyses of PM fractions obtained following complementary enrichment strategies and performed on an LTQ-Orbitrap instrument resulted in the identification of a total of 3090 proteins of which 2090 were unique hits. All three PM preparation methods developed in this work showed equally high capabilities regarding the enrichment of integral membrane proteins and provided complementary data. In our ongoing work, analyses of PM fractions are independently repeated to show reproducibility and to obtain further data. Up to 50percent of all proteins identified from PM fractions were membrane proteins with up to 21 predicted transmembrane domains of which approx. 50percent are known PM proteins and further 20percent are membrane proteins of so far unknown localization. Among the proteins identified were various most interesting candidates with high relevance to olfaction and neurobiology in general. In addition to G protein-coupled receptors and channel proteins we found a significant set of membrane proteins (e.g., Tmem proteins) of so far unknown localization and function that may be implicated in olfaction.
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