Heterogeneity in Genetic Control of Phenylalanine Metabolism in Man

Abstract

A HEPARINIZED blood sample was obtained from the antecubital vein just before the noon meal from twenty-five unrelated normal adult subjects and eighteen parents of eleven phenylketonurie probands. After deproteinization (plasma: picric acid, 0.427 N, 1 : 5 v/v). centrifugation and removal of the picric acid from the supernatant on ‘Dowex-2 × 8’ resin, a volume of the filtrate equivalent to 0.416 ml. of original plasma was applied to a 22 cm column of spherical resin of 13µ particle size and 7.5 per cent cross-linkage (Beckman–Spinco spherical resin, PA-35). Elution, at 50 ml./h, was performed on a modified Beckman–Spinco amino-acid analyser at 65° C with pH 4.25 sodium citrate buffer, 0.2 N, with respect to sodium^1,2. This procedure elutes tyrosine and phenylalanine as two discrete peaks at 51 and 55 min, respectively. The mean error of the method is ±2.1 per cent and ±1.7 per cent for tyrosine and phenylalanine, respectively; the recoveries are 100–103 per cent and 97–101 per cent, respectively, for the concentrations 0.01 to 0.20 µmoles (ref. 2).