The nature of apolipoprotein B in rat chyle.

Apolipoprotein B (apo B) is the integral apolipoprotein of chylomicrons, very-low-density lipoproteins (VLDL), intermediate-density and low-density lipoproteins. It is heterogeneous, occurring in two forms. In humans, the larger apo B-100 is formed by the liver in VLDL and the smaller apo B-48 is produced by the intestines in chylomicrons. In the rat, apo B-48 is also found in liver VLDL. Lee et ul. [ 1,2] reported small amounts of apo B-100 in rat chyle which disappeared on storage o r repeated Centrifugation. They suggested that proteinases, present in chylomicron preparations, were responsible for degradation of apo B-100 into apo B-48. However, it has also been shown that apo B-48 has thc same amino acid sequence as the N-terminal region o f apo BI00 and is formed from the same mRNA in intestine, apo €3-48 being released as a result of the action of a premature stop codon [ 3 ] . The nature of the origin of apo B-48 in chyle is of sufficient importance to warrant reinvestigation of the significance o f proteinase activity in generating this apoprotein. Malc Wistar rats (340-350 g) were tube fed 1.5 ml of corn o i l fortified with 10 i.u. o f a-tocopheryl acetate/ml as antioxidant. After 1 h they were anaesthetized with sodium pcntobarbital (60 mg/kg body weight) and the thoracic duct cannulatcd with polycthylene tubing. Chyle was collected in an ice bath in the presencc of final concentrations of 3 mM-