Major structural proteins of triacylglycerol-rich LIPOPROTEINS. There are two forms, apolipoprotein b-100 and apolipoprotein b-48, both derived from a single gene. ApoB-100 expressed in the liver is found in low-density lipoproteins (lipoproteins, ldl; lipoproteins, vldl). ApoB-48 expressed in the intestine is found in chylomicrons. They are important in the biosynthesis, transport, and metabolism of triacylglycerol-rich lipoproteins. plasma Apo-B levels are high in atherosclerotic patients but non-detectable in abetalipoproteinemia.