Muskelin distribution in whole brain cell extracts upon differential centrifugation. (A) Full length muskelin is abundant in the nuclear and cell remnant fraction (P1), the plasma membrane fraction (P2) and the respective supernatants (S1 and S2), which contain remaining membranes and the cytoplasm. Further separation reveals that relatively high amounts of muskelin are found in fraction P3, containing vesicular membranes and in fraction P4 that represents small vesicles and large protein complexes. In contrast, the soluble fractions S3 and S4 contain little muskelin. As controls, blots were detected against actin (loading control), with preimmune serum (antibody-specificity control) and with PSD-95, a protein known to be enriched at postsynaptic sites (P2) and at intracellular transport vesicles (P3). (B) The amounts of muskelin per fraction were quantitatively evaluated from three independent experiments using the NIH image software. For relative intensities, data were normalized against the respective actin signal, representing the relative amount of protein per lane. P: pellet; S: supernatant.