Complex sentence: It is a fat-binding proteion (apolipoprotein) that is part of the chylomicron and Intermediate-density lipoprotein (IDLs) that is essential for the normal catabolism of triglyceride-rich lipoprotein constituents.
Split into simpler sentences: It is a fat-binding protein (apolipoprotein) that is part of the chylomicron and Intermediate-density lipoprotein (IDLs). These are essential for the normal processing (catabolism) of triglyceride-rich lipoprotein constituents.