Apo B-100 is the major protein found in LDLs and a lesser constituent of IDLs and VLDLs (Table 18.1). It has a molecular weight of 513,000. The apoprotein B-48, which is found in chylomicrons, is a product of the same gene as Apo B-100 and contains identical amino acid sequence to the N-terminal half of Apo B-100. Apo B-100 is involved in binding lipoprotein complexes to the LDL receptor.