Summary
Lipoprotein(a) [Lp(a)] is recognized as an independent risk factor for atherosclerosis.
Lp(a) consists of a LDL-like moiety with an additional glycoprotein, apo(a), linked
to apolipoprotein B-100. Apo(a) has a high homology with plasminogen (Pg). In vivo,
Pg is activated on a fibrin surface by tissue Pg activator (tPA). We prepared Lp(a)
from plasma by sequential ultracentrifugation followed by lysine-sepharose affinity
chromatography. We found that a changing (donor dependent) fraction of the Lp(a) did
not bind to lysine-sepharose. This fraction, designated Lp(a)lys–, was further purified
using gel filtration. Bound Lp(a) [Lp(a)lys+] was eluted with 0.2 M EACA. Apo(a) isoforms
in both fractions were identical. In contrast Lp(a)lys+ inhibited Pg activation by
tPA in vitro (IC50% 20 mg/1), whereas Lp(a)lys– did not. In addition Lp(a)lys– did not bind to CNBr-digested
fibrinogen whereas Lp(a)lys+ did (K
d, app = 0.2 nM). Therefore we conclude that a changing donor dependent fraction of human
plasma Lp(a) does not inhibit Pg activation in vitro and does not bind to CNBr-digested
fibrinogen.