Biochemical features of major organ of Corti proteins (OCP-I and OCP-II) including partial amino acid sequence.

Further biochemical and biophysical characterization of two low-molecular-weight, strongly acidic proteins that are present at extremely high levels in the organ of Corti, tentatively named OCP-I and OCP-II, is presented. The two proteins are also present, although at much lower levels, in the vestibular end-organs and a variety of other inner ear tissues; they have not been observed in other systems. OCP-I and II are highly soluble and do not contain appreciable amounts of carbohydrate. The two proteins, originally described in the guinea pig, are compared electrophoretically with the corresponding proteins in several other mammalian species. Preliminary data on the amino acid composition of the two proteins are presented. Moreover, the amino-terminal sequence of a 22-residue segment of OCP-II is shown and compared to the sequences of known proteins.