Purification and complete amino acid sequence of beta-rat atrial natriuretic polypeptide (beta-rANP) of 5,000 daltons

A survey for natriuretic factors in rat atrial extract was performed by the aid of a simple assay for the relaxant effect on the contractility of chick rectum, in a manner similar to our previous purification of alpha-human atrial natriuretic polypeptide (alpha-hANP). Three distinct components (alpha, beta and gamma) of a potent relaxant activity with varying molecular weights, were found in the chromatographic regions of a crude extract. From the beta-component of rectum activity corresponding to about 5,000 daltons, a 48-amino acid peptide has been purified to homogeneity and found to elicit a potent natriuretic activity, when injected into the assay rats. Accordingly, the peptide was designated as "beta-rat atrial natriuretic polypeptide (beta-rANP)". The complete amino acid sequence of the peptide has been determined by microsequencing the S-carboxymethylated beta-rANP and its tryptic peptides.