Similarly, Michel et al. demonstrated the presence of different FS forms seen in human cerebrospinal fluid (CSF) in comparison to FS from porcine endothelial cells. The Fs proteins in CSF included 65-kDa and 78-kDa sizes. These authors hypothesize that the higher molecular weight proteins may be due to brain-specific posttransla-tional modifications or to an unknown substance that can cross-react with the anti-FS antibody. In developing bone, Funaba and colleagues identified a 55-kDa as well as a 50-kDa protein (under reduced conditions) for FS. When the same samples were studied for the presence of inhibin/ activin pA subunit, no 30-kDa or smaller band, namely a 14-kDa band consistent with the pA subunit alone, was identified (implying no activin or inhibin), only a 55- to 60-kDa band. No a subunit was detected with a antibodies. Therefore, the authors concluded that the bands represent precursor to activin or activin/FS complexes that do not dissociate even after SDS-PAGE. antibiotics levaquin
Given our findings of FS complexes in light of these other data, it is conceivable that, in vivo, after FS binds the ligand (either inhibin or activin), there is a conformational change in the structure of the proteins involved such that prolonged or aggressive reduction is necessary to break the complex into its components.