Detection of a beta-parvalbumin isoform in the mammalian inner ear

A small, acidic calcium-binding protein (CBP-15) has been detected in the guinea pig organ of Corti, the auditory receptor organ. The apparent molecular weight (15,000) and very low isoelectric point (pI approximately 3.1) suggest that CBP-15 is a beta-parvalbumin isoform. Consistent with this hypothesis, CBP-15 exhibits extreme homology to the mammalian oncofetal parvalbumin called oncomodulin. Sequence data have now been obtained for 30 residues in the N-terminal third of CBP-15. Identity with oncomodulin is observed at all 30 positions. This finding could necessitate revision of the assumption that postnatal mammals utilize a single alpha-parvalbumin isoform in muscle and nonmuscle settings alike.