Triglyceride-rich lipoproteins contain apoproteins including apoCII, apoCIII and perhaps apoA5 that regulate lipolysis. The lipoproteins must contact the vessel wall to allow the reaction to occur. Lipoprotein lipase (LpL) probably associated in part with heparan sulfate proteoglycans (HSPG) has its actions modulated by a number of factors including lipase maturation factor (LMF)1 that is needed to synthesize active enzyme, glycosylphosphatidylinositol-anchored high density lipoprotein-binding protein (GPIHBP) 1 that is necessary for securing active enzyme on the endothelial surface, and angioipoietin like protein 4 (ANGPTL4) that inhibits activity probably by dissociating the LpL dimer. Released fatty acids (FAs) enter cells either by non-receptor mediated pathways or via protein transporters such as FATPs, FABPpm, or CD36.