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(Arteriosclerosis, Thrombosis, and Vascular Biology. 1996;16:656-664.)
© 1996 American Heart Association, Inc.

Articles

A Quantitative Immunoassay for the Lysine-Binding Function of Lipoprotein(a)

Application to Recombinant Apo(a) and Lipoprotein(a) in Plasma

Jane L. Hoover-Plow; Nataya Boonmark; Pamela Skocir; Richard Lawn; Edward F. Plow

From the Joseph J. Jacobs Center for Thrombosis and Vascular Biology, Cleveland Clinic Foundation, Cleveland, Ohio, and the Department of Cardiovascular Medicine (N.B., R.L.), Stanford University, Stanford, Calif.

Correspondence to Jane Hoover-Plow, Department of Molecular Cardiology, Joseph J. Jacobs Center for Thrombosis and Vascular Biology/FF20, Cleveland Clinic Foundation, 9500 Euclid Ave, Cleveland, OH 44195.

Abstract Apo(a), the unique apoprotein of lipoprotein(a) (Lp[a]), can express lysine-binding site(s) (LBS). However, the LBS activity of Lp(a) is variable, and this heterogeneity may influence its pathogenetic properties. An LBS-Lp(a) immunoassay has been developed to quantitatively assess the LBS function of Lp(a). Lp(a) within a sample is captured with an immobilized monoclonal antibody specific for apo(a), and the captured Lp(a) is reacted with an antibody specific for functional LBS. The binding of this LBS-specific antibody is then quantified by using an alkaline phosphatase–conjugated disclosing antibody. The critical LBS-specific antibody was raised to kringle 4 of plasminogen. When applied to plasma samples, the LBS activity of Lp(a) ranged from 0% to 100% of an isolated reference Lp(a); the signal corresponded to the percent retention of Lp(a) on a lysine-Sepharose column but did not correlate well with total Lp(a) levels in plasma. Mutation of residues in the putative LBS in the carboxy-terminal kringle 4 repeat (K4-37) in an eight-kringle apo(a) construct resulted in marked but not complete loss of activity in the LBS-Lp(a) immunoassay. These data suggest that this kringle is the major but not the sole source of LBS activity in apo(a). The LBS-Lp(a) immunoassay should prove to be a useful tool in establishing the role of the LBS in the pathogenicity of Lp(a).

Key Words: lipoprotein(a) • lysine-binding site • recombinant apo(a) • functional immunoassay

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