Biosynthesis of apolipoprotein B in rooster kidney, intestine, and liver

After in vitro incubation with radiolabeled amino acids, extracts of various chicken tissues were screened for newly synthesized proteins reactive with antibody to plasma apolipoprotein B (apo B). An immunologically related protein was found in kidney as well as liver and intestine. This kidney protein showed the same mobility upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis as plasma apo B or pulse-labeled apo B made by liver or intestine. Partial proteolysis mapping with porcine elastase or V8 protease revealed nearly identical partial cleavage maps of pulse-labeled apo B from kidney, intestine, and liver. These data show that the kidney is a site of apo B synthesis and suggest that the kidney may be a significant source of plasma lipoproteins. Apo B synthesis was also detected in the distal small intestine and colon as well as in the proximal small intestine. The relative rate of apo B synthesis was 5% of total protein synthesis in the duodenum and decreased progressively to about 1% of protein synthesis in the colon. The synthesis of apo B in the distal small intestine and colon may indicate a similar capacity for dietary fat absorption via lipoprotein particles in all intestinal regions. The large intestine may be an additional source of plasma lipoproteins.