REDUCED DIMERIZATION OF LIPOPROTEIN-LIPASE IN POSTHEPARIN PLASMA OF APATIENT WITH HYPERCHYLOMICRONEMIA

As in post-heparin plasma of control subjects, post-heparin plasma of a patient with hyperchylomicronemia contained lipoprotein lipase (LPL) subunits with M(r) = 57000. But although the amount of LPL was the sa me as in post-heparin plasma of controls, no LPL activity was detectab le. Nearly all the LPL in post-heparin plasma of controls bound to hep arin-Sepharose and this LPL bound was mainly eluted with 1.5 M NaCl in parallel with the activity. In post-heparin plasma of the patient, 58 % of the LPL subunits did not bind to heparin-Sepharose and 23% was el uted with 0.6 M NaCl. Studies by sucrose density gradient centrifugati on showed that almost all the LPL in post-heparin plasma of controls w as recovered in the peak with a sedimentation coefficient of 6.8 S, co rresponding to the position of a dimeric form of LPL, in parallel with the activity; little LPL was recovered in the peak with a sedimentati on coefficient of 4.0 S, corresponding to the position of a monomeric form of LPL. In post-heparin plasma of the patient, 35% of the LPL sub units was recovered in fractions with larger sedimentation coefficient s at the bottom of the centrifuge tube, indicating the presence of an aggregated form(s) of LPL; the amount of the monomeric form of LPL was increased, while that of the dimeric form was decreased. Thus, defect of LPL activity in post-heparin plasma of the patient with hyperchylo micronemia could result from reduced dimerization of LPL subunits.