EFFECT OF CARBONYL CYANIDE M-CHLOROPHENYLHYDRAZONE (CCCP) ON THE DIMERIZATION OF LIPOPROTEIN-LIPASE

Lipoprotein lipase (LPL), an enzyme playing the central role in trigly ceride metabolism, is a glycoprotein and a homodimer of identical subu nits. Dimerization and proper processing of oligosaccharide chains are important maturation steps in post-translational regulation of enzyme activity. Indirect evidences suggest that dimerization of LPL occurs in endoplasmic reticulum (ER) or Golgi. In this study, we investigated the dimerization status of LPL in 3T3-L1 adipocytes, using sucrose de nsity gradient ultracentrifugation and carbonyl cyanide m-chlorophenyl hydrazone (CCCP), an inhibitor of ER-Golgi protein transport. In the p resence of CCCP, no increase of cellular LPL activity was detected dur ing 2 h of recovery period after the depletion of LPL with heparin and cycloheximide. Only endoglycosidase H (endo H)-sensitive subunits wer e found in CCCP-treated cells after endo H digestion, suggesting that inactive LPL was retained in ER. In the presence of castanospermine, a n inhibitor of ER glucosidase I, LPL subunits of both control and CCCP -treated cells had same molecular weight, indicating that complete oli gosaccharides were transferred to LPL subunits in the presence of CCCP . In sucrose density gradient ultracentrifugation, all the LPL protein synthesized in the presence of CCCP was found at the dimeric fraction s as in control cells. Most of LPL protein in control cells showed hig h affinity for heparin, and there was no difference between the contro l and CCCP-treated cells. These results suggest that dimerization and acquisition of high affinity for heparin of LPL can occur in ER of CCC P-treated cells without acquisition of catalytic activity.