236 P. SOUPART 
order of the average concentrations is quite similar in the two groups. On com- 
parison of Figs. 5 and 6, the following differences may be distinguished: (1) average 
concentrations are in general a bit lower in infants than in adults; (2) the range of 
variation tends to be larger in infants than in adults; (3) there are some amino 
acid concentrations in infants which differ markedly from what they are in adults, 
namely that of half cystine plus cysteine and that of glutamic acid and glutamine. 
400 
po /| ‘ 
plasma 
350 
300 
250 

200 
150 
100 
50 


6 ° d S b O 
oO ~> = - i uw = S} 1o1) ) >} iJ = wv uv ” 
= oO. te 2 Ys ay - Ce fe S Sas = oe ss == =) a 2 
< > - a wn ee <a 25 = 10° (o) = = ao 2 =z Ss Ss Vv at S 
ros fs N 
< ae i a 
CG 
Glu &Glu NH» 
Fig. 6. Free amino acid plasma levels in normal children. Open circles indicate variation range 
observed and filled circles average values. For cystine, glutamine and glutamic acid see text*. 
Straight line shows glutamic acid levels variation range and dotted line that of glutamine. Both 
groups are made of minimal approximate values (see p. 222). 
Half cystine plus cysteine being of medium abundance (70-108 ymoles/l of plasma) 
in adults, this amino acid is present only as traces in children’s plasma*. Glutamic 
acid and glutamine values found have to be considered as a special case, owing to 
the causes of error which interfere with their determination as previously indicated. 
The concentrations given here are thus to be taken as minimal values. In plasma the 
* In the present data, cysteine has been oxidized into cystine prior to analysis because 
cysteine does not react with ninhydrin. It is only recently (1960) that a method has been worked 
out by BricHaM, Moore anp STEIN! which affords for the separate determination of cysteine 
and cystine, the former under the form of carboxy-S-methylcystine, by means of ion-exchange 
chromatographic analysis. 
References p. 261/262 
