BNP-45 represents the 45 amino acids at the C-terminus and the mouse BNP-45 has all the amino acid residues thought essential for NP bioactivity, although sequence identity when studied with other BNP hormones (rat, 64%; dog, 53%; pig, 50%; and human, 44%) was clearly less than the identity among ANF hormones. Further, sequence identity between rat and mouse BNP prohormones is found to be more conserved in the N-terminal portion of the prohormone than in the C-terminal BNP-45 (88% versus 64%). The threonine 81 residue at which a protein kinase C phosphorylation site is present in the putative mature mouse BNP-45 hormone is not conserved in the rat sequence. Comparing the amino acid sequence surrounding the proteolytic processing site for BNP-32 in human, pig, and dog BNP with the corresponding site for BNP-45 in the rat and mouse sequence we find that all of the secreted BNP hormones have an N-terminal serine preceded by an arginine in the prohormone sequence, and the mouse and rat sequences are highly conserved at the putative scissile bond (LKRVLR-SQ). Further comparative sequence analysis indicates that an arginine being present at position -4 relative to the scissile (R-S) bond in all mammalian BNP precursors. Thus, processing of BNP prohormones to both BNP-45 in rodents and BNP-32 in higher mammals appears to require a protease with a conserved recognition sequence (RXXR-S). Also, the conserved sequences in the BNP prohormones matches the consensus cleavage site for human furin, a calcium-dependent serine endoprotease expressed in mouse heart, and possibly having a role in processing BNP precursors.