Isolation and structural analysis of the circulating human cardiodilatin (alpha ANP)

A new method was applied to isolate a polypeptide hormone from human blood. The polypeptides from 1,000 1 of hemofiltrate with a molecular weight lower than 20 kDaltons were adsorbed to 2.5 kg alginic acid, then eluted, precipitated, and desalted on a G-25 Sephadex column, thus obtaining a crude lyophilised plasma polypeptide extract. These polypeptides were further submitted to ion-exchange chromatography. Thereafter, two steps of HPLC were carried out to purify a distinct polypeptide which was the circulating form of cardiodilatin (CDD) in this case. The amino acid analysis, C-terminal enzymatic cleavage by carboxypeptidase A, and sequence analysis showed that the only form of circulating cardiodilatin is the 28 amino acid residue containing molecule, cardiodilatin-99-126 cleaved from the C-terminus of cardiodilatin-126 and identical with alpha-ANP (alpha atrial natriuretic polypeptide). Other bioactive molecular forms of the polypeptide hormones of the cardiodilatin family were not detected in the hemofiltrate. The isolation procedure was followed up by a bioassay using in vitro vascular smooth muscle relaxation.