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

Abstract

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.