Pro-Apolipoprotein A-I to Apolipoprotein A-I Converting Activity Between Normal and Tangier Plasma

Abstract. We examined the ability of the plasma of a 52-yr-old male Tangier patient to effect the conversion of radiolabeled pro-apolipoprotein A-I (apo A-I), isolated from hepatoma cell culture media, into mature apo A-I. The conversion was assessed by amino-terminal sequence analysis, isoform patterns with two-dimensional gel electrophoresis, and a rapid assay based on the different solubilities of intact pro-apo A-I and its hexapeptide prosegment in 10 % trichloroacetic acid. We found that the converting activity of Tangier plasma was comparable to that exhibited by control normoli-pidemic plasma and that in both cases pro-apo A-I was correctly processed at the Gln-Asp bond. After ultracen-trifugal fractionation of Tangier plasma at d = 1.21 g/ml, the pro-apo A-I-to-mature apo A-I converting activity was mainly recovered in the middle fraction of d = 1.225 g/ml and was at least 10-fold more effective than the top and bottom fractions. In contrast, in normal plasma the activity was only present in the top and bottom fractions. It has been previously established that in Tangier plasma the pro-apo A-I/apo A-I ratio is significantl