FORMS OF LIPOPROTEIN-LIPASE IN RAT-TISSUES - IN ADIPOSE-TISSUE THE PROPORTION OF INACTIVE LIPASE INCREASES ON FASTING

Previous studies have shown that the ratio of lipoprotein lipase (LPL) catalytic activity to LPL mass in tissues differs in different condit ions, but it is not clear whether this occurs by a change in the catal ytic efficiency of the LPL molecules, or because of a shift in the rel ation between active and inactive forms of the enzyme. To explore this , we have measured LPL activity and mass in detergent extracts of rat tissues. LPL specific activity was high and similar in heart, skeletal muscle, lung and brain. The liver had significantly lower specific ac tivity, which is in accord with previous findings that the liver takes up and catabolizes LPL. The specific activity was also low in adipose tissue from fasted rats. When tissue extracts were applied to columns of heparin-agarose and eluted by a gradient of NaQ, a peak of active LPL was eluted at 1.0 M NaCl, but there was also a peak of inactive LP L protein, which was eluted at 0.6 M NaCl. In adipose tissue, LPL acti vity decreased by 70-80% during an overnight fast, whereas LPL mass de creased by only 20-40%. The mass ratio between inactive and active LPL , as separated by heparin-agarose chromatography, increased from 0.5 t o over 2 during the fast. In hearts there was no significant differenc e between fed and fasted rats in total LPL activity, LPL mass or in th e distribution between inactive and active forms. The results indicate that the relation between inactive (probably monomeric) and active (d imeric) forms of LPL is a target for post-translational regulation in adipose tissue.