Evidence that Lp[a] contains one molecule of apo[a] and one molecule of apoB: evaluation of amino acid analysis data

Abstract

Amino acid analysis was performed on four Lp[a] preparations to evaluate whether or not the amino acid data was consistent with Lp[a] containing one molecule of apolipoprotein[a] [apo(a)] linked to one molecule of apoB-100. Amino acid analysis was carried out in duplicate on a Beckman model 121 amino acid analyzer. Apo[a] size was determined by a high-resolution agarose gel electrophoretic method that provides an estimate of apo[a] kringle 4 repeats. When Lp[a] was assumed to contain one apo[a] and one apoB molecule per particle, the average absolute bias between the expected molar percentage of each amino acid, as based on the known sequence of apo[a] and apoB, and the obtained molar percentage ranged from 2 to 3.5%. In contrast, by assuming two molecules of apo[a] and one of apoB per Lp[a] particle, the bias between the expected and observed molar percentage ranged from 8.5% to 10%, and by assuming one apo[a] and two apoB the bias ranged from 8.8% to 11.4%. Comparison of Lp[a] concentrations, calculated from six stable amino acids and the Lp[a] composition predicted from the known sequence, was in excellent agreement (bias ranging from 0.3% to 0.9%) with the Lp[a] concentration calculated from the sum of the amino acid concentrations, when Lp[a] was assumed to contain one molecule of apo[a] and one molecule of apoB. However, there was poor agreement (7.4% to 8.4% bias) when it was assumed that Lp[a] contains two molecules of apo[a] and one molecule of apoB. These results indicate that the evaluated Lp[a] preparations contain one apo[a] per Lp[a] particle. Evaluation of amino acid analysis data provides a relatively simple approach to determine the molar ratio of apoB to apo[a] in Lp[a] and provides evidence that Lp[a] contains one molecule of apo[a] and one molecule of apoB.