Identification in rat atrial tissue of multiple forms of natriuretic polypeptides of about 3,000 daltons

Rat atrial natriuretic peptides of relatively low molecular weight have been isolated from the alpha-component of rectum relaxant activity corresponding to about 3,000 daltons, which was obtained as a side fraction in our previous isolation of beta-rat atrial natriuretic polypeptide (beta- rANP ). In contrast to the same fraction from human atria, the rat atrial alpha-component was found to contain six or more distinct but related peptides, eliciting a potent natriuretic activity. Six of them (B-II, C, D, E, B-I and A), containing 35, 33, 32, 31, 28 and 25 amino acid residues, respectively, have been purified to homogeneity and sequenced. All these peptides were found to correspond to the C-terminal sequence of beta- rANP composed of 48 residues, with varying N-terminal elongations. This indicates that these peptides are derived from beta- rANP . Peptide B-I, composed of 28 residues, is identical to alpha-human atrial polypeptide(alpha- hANP ), with a single replacement of Ile for Met at position 12.