COMPARISON OF [5,5,5-H-2(3)]LEUCINE AND [RING-H-2(5)]PHENYLALANINE TRACERS FOR THE MEASUREMENT OF HUMAN APOLIPOPROTEIN B-100 KINETICS

Incorporation of amino acids labeled with stable isotopes in apoliprop roteins is used to estimate kinetic aspects of lipoprotein metabolism, In this study two deuterated tracers, [5,5,5-H-2(3)]leucine and [ring -H-2(5)] phenylalanine, were compared. Isolation and acid hydrolysis o f apolipoproteins are required for mass spectrometric analysis. When a polipoprotein B-100 of very low density liproproteins was prepared wit h this procedure, a loss of deuterium was observed on deuterated pheny lalanine with 10 and 6 M HCl hydrolysis but not with deuterated leucin e or when 4 M HCl hydrolysis was used. This study stresses the effect of acid hydrolysis on [ring-H-2(5)] phenylalanine. This tracer must be used with caution in studies of specific protein synthesis.