N-terminally extended form of C-type natriuretic peptide (CNP-53) identified in porcine brain.

C-type natriuretic peptide of 22 residues (CNP-22) is very recently identified in porcine brain as a third member of the mammalian natriuretic peptide family (1). Using a radioimmunoassay system newly established for CNP-22, we searched for CNP-related peptides in porcine brain. In addition to CNP-22, one major form of immunoreactive CNP was detected in porcine brain extracts, being isolated by immunoaffinity chromatography and reverse phase high performance liquid chromatography. By microsequence analysis, the peptide was deduced to be a 53-amino acid peptide carrying a CNP-22 sequence at the C-terminus, and was designated C-type natriuretic peptide-53 (CNP-53). CNP-53 was found to be a major molecular form of CNP in porcine brain.