Composition and supramolecular organization of the tectorial membrane

We have shown that collagen accounts for approximately 40% of the total protein of the tectorial membrane (TM) of the guinea pig and have estimated several essential parameters of TM composition including dry weight, wet weight, and water content. The major collagenous protein was definitively identified as type II collagen by SDS-PAGE, CNBr peptide mapping, and immunoblot assays. Quick- freeze, deep-etch electron microscopy of the guinea pig TM demonstrated a dense meshwork of fibers embedded in a complex microfibrillar matrix which may consist of proteoglycans; the larger fibers were similar in size and appearance to type II collagen fibers of elastic cartilage. Finally, the comparative free’amino acid profiles of TM strongly suggest that the TM is chemically transparent with respect to endolymph. Thus, the TM appears to consist of a highly hydrated matrix mechanically stabilized by type II collagen fibers. The possible physicochemical and functional significance of these findings for sound transduction is discussed.