ENZYMATIC-PROPERTIES OF ACTIVE FORM OF HUMAN APOLIPOPROTEIN(A)

Lipoproteins (d=1.05-1.12 g/ml) were obtained from pooled serum by density gradient ultracentrifugation and used as a source for isolation of apolipoprotein (a) (apo(a)). It was found that both these lipoproteins and purified apo (a) possess negligible amidolytic and proteolytic activity. After preincubation of lipoproteins and apo (a) with collagen-Sepharose, the increase in enzymatic activity was observed. The activation of purified apo (a) also occurred upon its storage in the cold. After two week storage at 7°C, the amidase activity, as measured by splitting of the substrate D-Pro-Phe-Arg-pNA, was increased from 0.009 U/mg to 0.85 U/mg. The amidase activity was completely inhibited by phenylmethylsulfonyl fluoride (10-3M) and by soybean trypsin inhibitor (10-5M); it was not inhibited by aprotinin (10-6M). Activated apo (a) did not split azocasein but converted plasma prekallikrein to kallikrein and degraded apolipoprotein B-100. © 1990.