Clearing Factor Lipase and Its Role in the Regulation of Triglyceride Utilization. Studies on the Enzyme in Adipose Tissue

Abstract

It is now generally accepted that the main physiological function of the enzyme clearing factor lipase, or lipoprotein lipase, is to facilitate the uptake of triglyceride fatty acids (TGFA) from the blood by the extrahepatic tissues (1). This function is thought to be exercised through the initiation by the enzyme of the hydrolysis of chylomicron and very low density lipoprotein triglycerides that are sequestered at the luminal surface of the endothelial cells of the blood capillaries. Furthermore, changes in the activity of the enzyme that occur in particular tissues with changes in physiological status are believed to be responsible for corresponding changes in the uptake of the plasma TGFA by these tissues. Thus, the enzyme probably also performs a directive function in determining the pattern of TGFA removal from the bloodstream. In view of this proposed secondary role of clearing factor lipase, it is clearly important to elucidate the factors which control, and the mechanisms which underlie, the changes in its activity. These questions are considered here in relation to the enzyme in adipose tissue. The activity in this tissue is known to fall markedly on starvation and to rise again on refeeding, and these changes can be directly correlated with corresponding changes in the ability of the tissue to take up TGFA from the bloodstream.