COMPARISON OF GUINEA-PIG SERUM-LIPOPROTEINS AFTER IODINATION BY 2 DIFFERENT METHODS

Guinea-pig low-density lipoproteins were isolated by ultracentrifugation and iodinated either by the ICl method or by the chloramine-T procedure. The efficiency of labelling by both methods was essentially the same. When the 2 products were compared by ultracentrifugation, gel chromatography and immunodiffusion analysis, no significant difference in their properties was detected. When they were compared by gradient-gel electrophoresis, aggregates were found in the product of the ICl method, but not in the lipoprotein iodinated by the chloramine- T process. Both products were metabolized by the guinea pig with essentially the same fractional catabolic rate. The fractional catabolic rate of lipoprotein iodinated by the chloramine-T method was not significantly different from that of lipoprotein biologically labelled in the protein moiety with [75Se]selenomethionine. It is concluded that the products of both methods of iodination are almost equally acceptable, provided that the optimum conditions for the chloramine-T reaction are carefully established.