The complete amino acid sequence of proapolipoprotein (proapo) A-I of chicken high density lipoproteins was determined by sequencing overlapping peptides produced by trypsin, S. aureus V8 protease, and cyanogen bromide cleavage. There are 240 amino acid residues in mature chicken apoA-I. By direct sequence analysis of a cyanogen bromide peptide, we also determined the sequence of a 6-amino-acid prosegment which is present at approx. 10% the molar amount of the mature peptide in chicken plasma. Sequence comparison among apoA-I from chicken, human, rabbit, dog and rat, and secondary structure analysis indicate that while the degree of sequence homology is only moderate ( < 50% between chicken and man), there is good conservation of apoA-I secondary structure, especially in the N-terminal two-thirds of the protein in these widely separated species.
