OCCURRENCE OF FREE AMINO ACIDS — VERTEBRATES 509 
DISCUSSION 
Chairman: GEORGE ROUSER 
Mayron: Dr. SCHREIER, was free sialic acid found in either the blood or urine? 
SCHREIER: One can find sialic acid in urine with special methods. 
H. ROSENBERG: Dr. SOUPART, you mentioned the possibility that ultrafiltration might liberate 
amino acids that are adsorbed to proteins. Could you comment on this any further? I do not quite 
see how this could possibly happen, because you would not get a dilution or concentration of any 
filterable material during the entire process. 
SouparRT: I was only suggesting that our present concept of renal handling of amino acids 
should be carefully reinvestigated in the light of the following facts. When considering the renal 
handling of plasma free (or so-called free) amino acids, it is generally assumed that they pass 
freely into the glomerular filtrate and are present in this filtrate at the same concentration as in 
the plasma, but this assumption has not been experimentally demonstrated up to now for obvious 
reasons. Moreover, what we call blood plasma free amino acid concentrations are values deter- 
mined on plasma filtrates obtained by use of various deproteinization methods, such as a 1% 
picric acid solution. These procedures might well be able to break weak bonds linking amino acids 
to protein carriers. That such a possibility has to be kept in mind is suggested by recent papers of 
Dr. McMenamy!?” and his group in Boston, who claimed that there is evidence for protein binding, 
especially in the case of tryptophane, which they say is largely bound to albumin. As suggested by 
other speakers at this conference, “‘free’’ amino acid binding to other structures seems to happen 
quite often in tissues. If substantial evidence could be obtained that such a binding occurs in 
blood plasma, our present concept of the renal handling of “free’’ amino acids would have to be 
revised. I would also emphasize the fact that when preparing a sample for plasma free amino acid 
analysis one has to deproteinize the plasma immediately after the blood is drawn from the vein, 
because there is a possibility that free cysteine tends to combine with -SH groups of the plasma 
proteins. 
RouseEr: I think it is interesting that tryptophane binding by plasma protein has been reported. 
Apparently it did not occur as a general phenomenon, and I would not expect this to be important 
with cystine except by disulfide exchange. 
PERRY: I wanted to make one comment about Dr. WESTALL’s paper, concerning amino acids in 
cerebrospinal fluid. We have had the opportunity in our laboratory to study pools of normal adult 
cerebrospinal fluid and cerebrospinal fluid from children with various genetically determined forms 
of mental defect using the MoorE AND STEIN technique. We were surprised to find no trace of 
y-aminobutyric acid at all, so that even though the brain is rich in y-aminobutyric acid and cere- 
brospinal fluid is formed by the brain and bathes it, none appears in the cerebrospinal fluid. 
One other comment I might make is to emphasize the remarks of Dr. SoupARtT about the importance 
of deproteinization. We found no trace of cystine in cerebrospinal fluid and finally concluded that 
it was because we failed to deproteinize immediately. Even though one deproteinizes cerebrospinal 
fluid 24 hours after it is withdrawn, and keeps it at 20° during that period, one still loses all of 
the cystine through sulfhydryl binding to protein. 
Prez: I would like to clarify a question brought up by Dr. WEsTALL concerning the free amino acids 
in saliva. A spot seen on chromatograms has been identified by some as y-aminobutyric acid. 
Dr. Fospick and I showed some years ago that this material is not y-aminobutyric but hasa behavior 
closer to the next higher homologue, a-aminovaleric acid. More important is the fact that this is 
not a natural constituent of saliva, but a result of bacterial action in the mouth. In fact, almost 
all of the free amino acids in saliva arise from that source. The only exception, I think, is phospho- 
ethanolamine, which is found in pure parotid saliva. 
SHAW: I would like to say a few words concerning Hartnup disease, which was discussed earlier 
by Dr. WEsTALL. We have been able to carry out some studies at Cal Tech on Hartnup disease through 
the courtesy of Professor DENT, and we find that the abnormal pattern of urinary indole com- 
pounds which has been described in this disorder results from the action of intestinal micro- 
organisms on dietary tryptophane. When neomycin is administered in small doses the abnormal 
indoles disappear entirely. Other evidence points to a defective transport of amino acids as the 
key factor in this disorder. 
References p. 511 
