The primary structure of apolipoprotein A‐I from rabbit high‐density lipoprotein

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Abstract
The amino acid sequence of rabbit apolipoprotein A‐I (apo A‐I) has been determined by degradation and alignment of two overlapping sets of peptides obtained from tryptic and staphylococcal digestions. All of the peptides of rabbit apo A‐I resulting from digestion by staphylococcal protease were isolated and sequenced except residues 33–37. A digestion with trypsin was employed to find overlapping and missing peptides. The N‐terminus of rabbit apo A‐I was confirmed by sequencing the intact protein up to 20 residues while the C‐terminus was identified through its homology with human apo A‐I. The protein contains 241 residues in its single chain. Its primary structure is highly homologous to the reported canine apo A‐I (80%) and human apo A‐I (78%), but exhibits less similarity with rat apo A‐I (60%). Like human apo A‐I, rabbit apo A‐I contains very little histidine (2) and methionine (1); it does however have two residues of isoleucine. Based on a comparison of the hydrophobichydrophilic character of apo A‐I residues with that of the two synthetic peptides that activated lecithin:cholesterol acyltransferase (Pownall et al. and Yokoyama et al.), we found that the five segments with the highest corresponding homologies on the protein are located within the N‐terminal half. This suggests that the N‐terminal half of apo A‐I contains the major portion of regions activating lecithin:cholesterol acyltransferase.

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