Primary structure of a high Mr form of rat atrial natriuretic factor

During the purification of rat atrial natriuretic factor (ANF), low, intermediate and high Mr forms were observed. In this report we describe the purification and amino acid sequence of a 73 residue peptide containing at its C-terminus the previously sequenced 33 amino acid ANF peptide. The cleavage necessary to produce the 33 amino acid ANF from the 73 amino acid precursor occurs at a Leu-Leu bond. We also report the amino acid composition of an even longer form of ANF containing about 103 residues, in which the extension is amino terminal to the 73 peptide. A computer data bank search showed that the determined sequence is a novel one and is not homologous to any known proteins or segment thereof. The natriuretic activity of the 73 amino acid form when compared to that of a synthetic ANF peptide, comprising the sequence of the last 26 amino acids of ANF, was found to be slightly lower.