FREE AMINO ACIDS OF BLOOD AND URINE 221 
as “free amino acids” is by no means a simple and logical concept but a conventional 
and provisional one, depending largely on the nature of the method used for the 
purpose of amino acid separation and determination. The author's laboratory has 
specialized very early (1950) in the analytical use of ion-exchange chromatography 
and accordingly all experimental data submitted below have been obtained by one 
or other variant of the MOORE AND STEIN ion-exchange chromatographic method. 
The group of substances referred to here as “free amino acids” has thus to be defined 
in terms of ion-exchange analysis. It includes free amino acids, substituted free 
amino acids or amino acid derivatives in which the amino group stays free, enabling 
them to react with ninhydrin. Examples of such substances are taurine, glutamine, 
or asparagine (the last two being amino acids combined with ammonia) or tyrosine- 
O-sulphate?, an amino acid combined with sulfuric acid by a linkage which does not 
involve the amino group. The group also includes alcohol amines which are other 
types of amino acid derivatives in which the amino group remains free, for instance 
ethanolamine, which corresponds to decarboxylated serine. Chromatographic sepa- 
ration on ion-exchange columns occurs when unhydrolyzed urine is used and these 
substances are detected by means of the ninhydrin reaction. Additional peaks 
show up on elution curves obtained from unhydrolyzed urine, comprising urea, 
ammonia, probably also small amounts of peptides (BOULANGER AND BISERTE®*: 4; 
WESTALL®) and eventually still unidentified amino acids but, for obvious reasons, 
these substances are not included in the group referred to here as “free amino acids”. 
On the other hand, the term “aminoaciduria” has not been consistently used with 
the same meaning. In the past Io years, according to certain clinical biochemists, 
it referred to pathological conditions only, just as the word uremia refers to a disorder 
and not to blood-urea level in general. It is also used in a broader sense, referring to 
amino acid excretion in general, whether it is normal or not, in the same way as 
the word glycemia is used. In this report, the term “aminoaciduria” will be used 
in the latter sense since there is a significant output in normal conditions and since 
there are normal conditions in which amino acid output may be different than 
usual, although the condition is not pathological, an instance of which is found 
in the hyperaminoaciduria which occurs in the course of normal pregnancy’. 
MATERIAL AND METHODS 
Ion-exchange chromatography 
Ion-exchange chromatographic method, as worked out by S. Moore Anp W. H. 
STEIN, is presently the most satisfactory method for amino acid analysis. According 
to the chronological development of this method, four different procedures may be 
distinguished : 
a) 1951 method on Dowex-50-X8 columns’, which is suitable for protein-hydro- 
lyzates analysis. 
b) 1954 method on Dowex-50-X4 150-cm column’: °, which is particularly adapted 
to complex physiological fluids analysis. 
c) 1958 method on Amberlite-I[R-120 column?®, also well adapted to physiological 
fluids analysis but characterized by an increased speed of operation. 
d) 1958 completely automatic procedure on Amberlite-[R-120-X8 150 and 
References p. 261/262 
