Analysis of Apolipoprotein A-I Synthesized in Vitro from Chick Intestinal mRNA

In man and in many laboratory animals including the chick apolipoprotein A-I (apo A-I) is the main constituent peptide of plasma high density lipoproteins (HDL) (1–5). In all species examined so far apo A-I is synthesized in liver and intestine (6–8) as a precursor molecule (pre-proapo A-I) which is characterized by an ami-noacid extension at its NH terminal end (signal peptide). Part of this sequence is cleaved co-translationally to originate the intracellular precursor of apo A-I (proapolipoprotein A-I) (9–15). In man and rat the latter is secreted into the blood stream where is converted to the mature extracellular form by the action of some plasma protease(s) (16–19). It has been reported that in man (20–25), rat (25), mouse (24), rabbit (25) and chick (15) plasma apo A-I consists of a family of isoforms which have the same molecular weight, react equally well with anti apo A-I antiserum, but have different isoelectric points. The relative content of each isoform spans over a wide range (from 1–2% for the minor isoforms to 60–70% for the major ones) and shows a high degree of species difference (25).