A NOVEL ANTISERUM SPECIFIC TO APOLIPOPROTEIN-B-48 - APPLICATION IN THE INVESTIGATION OF POSTPRANDIAL LIPIDEMIA IN HUMANS

1. Apolipoprotein B-48, the transport protein for chylomicrons, is ide ntical with apolipoprotein B-100 for the first 48% of its sequence. No antiserum has yet been reported that can recognize apolipoprotein B-4 8, but not apolipoprotein B-100. 2. In the present study an antiserum was raised to the C-terminal sequence of apolipoprotein B-48, using sp ecific chemical reactions to ensure that the charged carboxyl group of the C-terminal isoleucine residue was free. In a Western blot the ant iserum was shown to bind to a protein band having the characteristics of apolipoprotein B-48, but not to apolipoprotein B-100. 3. In the ear ly evening 11 subjects were given a test meal which contained 40 g of mixed oil and retinyl palmitate. Blood samples were collected over 9 h . Chylomicron-enriched fractions were prepared and analysed for triacy lglycerol, retinyl palmitate and apolipoprotein B-48, the latter after separation using SDS/PAGE and visualization by chemiluminescence on a Western blot. Both triacylglycerol and apolipoprotein B-48 showed an early peak at 1 h, which was not seen with retinyl palmitate. All thre e substances gave a broader peak between 5 and 6 h post-prandially. Re tinyl palmitate concentrations declined rapidly during the late (6-9 h ) postprandial period, but apolipoprotein B-48 concentrations remained elevated. 4. This study has shown that an antiserum has been produced which is specific for apolipoprotein B-48. This has enabled measureme nt of postprandial concentrations of the protein that revealed feature s of chylomicron metabolism which have not been reported previously.