FREE AMINO ACIDS OF BLOOD AND URINE 247 
easily, although they are so similar in structure? Why are amino acids of small 
molecular weight such as glycine and alanine kept within the erythrocytes when 
their molecular weight, so close to that of urea, should allow them presumably to 
pass rather easily through the erythrocyte membrane? The case of aspartic and 
glutamic acids might probably be explained by the fact that erythrocytes contain glu- 
tamic—oxalacetic and glutamic—pyruvic transaminase systems. 
From the data presented in Table VII, one may try to figure out a tentative 
quantitative model for distribution of free amino acids between the different com- 
partments of the whole blood reservoir. Comparison of the free amino acid concen- 
trations in the three types of formed elements to those found in plasma is impressive, 
but does not reflect what amounts are actually present. Such an evaluation may 
be obtained by assuming theoretical values for the different compartments, for 
instance, a mean whole blood volume of 61, an hematocrit value of approx. 50%, 
leucocytes and platelets volumes of respectively 1 and 0.5% of the whole blood 
volume. When such calculation is made, as shown in Table X, one can roughly 
evaluate the relative total content of the four compartments of the blood in the follow- 
ing way: 
DABLE X 
TENTATIVE DISTRIBUTION OF FREE AMINO ACIDS IN THE FOUR COMPARTMENTS 
OF THE BLOOD RESERVOIR IN MAN 






: Blood- Jrinary Plasma 
Apne Flasinane yi ACOH n= Lenanonies.. (Platelets. oe clearance 
(umoles* ) 5 ; (umoles/24 h***) time§ 
Taurine 120 95 1200 560 990 sy lat 
Lysine 548 264 103 34 50 Ir days 
Glycine 666 740 266 133 1380 12 ein 
Alanine 1124 750 337 112 240 5 days 
Valine 726 700 nit 43 go g days 
Leucine 382 760 305 76 80 5 days 
Isoleucine 229 75 114 38 Ilo 2 days 
Serine 286 230 238 95 400 7p lobe 
Threonine 330 330 168 2 150 2 days 
Phenylalanine 152 75 121 30 80 2 days 
Tyrosine 166 105 83 28 110 1.5 day 
Histidine 2260 300 2 9 goo 6 h 
Arginine 258 60 14 15 30 8.5 days 
Aspartic acid 7 710 150 75 60 3) al 
Glutamic acid (136) (612) (340) (68) (500) ? 
Methionine 67 o? 67 7 50 1 day 
Cystine #/, 292 o? 16 o? 120 2.5 days 
Proline 608 350 86 43 oO == 
Total 6369 6162 3811 1408 5340 — 
% of whole 
blood volume +50% +50% e/a Ols% -- — 


* Average values calculated from STEIN AND Moore data!™. 
** Calculated from data shown in Table VII. 
*** Average values in man according to SOUPART??. 
§ Urinary daily output divided by amount contained in plasma, expressed in h or days. 
Indicates time necessary for loss by urinary excretion of the amount normally present in plasma. 
* and ** calculated for a theoretical whole blood volume of 61. 
References p. 261/262 
