194 OCCURRENCE OF FREE AMINO ACIDS — COMPARATIVE ASPECTS 
DISCUSSION 
Chairman: NORMAN H. Horowi1rz 
AwaAPaARA: I would like to ask Dk. ROSENBERG a question on the formation of ethanolamine. So far 
as I know, no one has yet shown a serine decarboxylase. It is very apparent from in vivo evidence 
using double labeled material that serine gives rise to ethanolamine. There is no doubt then that 
serine first combines in some form, perhaps in nucleotides similar to those you have mentioned, 
and that it can then be decarboxylated. It is quite appalling, however, that the so-called serine 
decarboxylase has not been demonstrated. Do you have any information on that? 
H. ROSENBERG: I| believe a very recent communication has shown that phosphatidyl serine and 
ethanolamine are interconvertible; perhaps someone has seen this paper. 
RouseErR: What happens, presumably, is that phosphatidyl ethanolamine undergoes an exchange 
with serine to make phosphatidyl serine which is then decarboxylated back to phosphatidyl 
ethanolamine. In this way ethanolamine is released, and in the cycle serine is converted (decarboxy- 
lated) to ethanolamine while combined in a phospholipid. 
GurRoFF: In our laboratory GIBSON AND WILSON were able to show that serine phospholipids 
could be decarboxylated and methylated all the way to the choline phospholipid in liver prepara- 
tions. I think this has also been done in DR. GREENBERG’s laboratory. 
LorTFIELD: I would just like to ask either of the marine invertebratologists here whether the 
correlation between taurine content and the nature of the beast is related to whether they are in 
marine conditions. You said some brackish water animals had very low taurine, and I was wonder- 
ing whether they would begin to accumulate taurine, if you put them into isotonic salt. In other 
words, is the possession of taurine only a reflection of the effect of the environment on their 
capacity to retain this substance? 
AwAPARA: We tried to do this but, unfortunately, the animal died very quickly. The only one 
tried was Rangia cuneata, a clam, which lives in brackish water. We managed to put it in much 
higher concentration of salt water, but the evidence was very erratic. I believe that the idea is 
correct. 
KITTREDGE: Justa point on the ionic strength of the medium. In attempting to force the synthe- 
sis of taurine from radioactive sulfate, we took abalone and brought them rather rapidly down to 
about half the normal ionic concentration of their environment, and then back up to higher than 
normal concentrations. We found, as Dr. AwAPARA mentioned, that marine invertebrates retain 
their taurine very tenaciously. The tissues would become flooded with excess water during ex- 
posure to sea water with low ionic concentration, but in no case could we drastically change the 
tissue content of taurine or force synthesis of new taurine from sulfate. 
H. RosENBERG: I would just like to add here that we find quite a lot of taurine in the earth- 
worm, which is a terrestrial polychaete, and there is also quite a lot in the bird. In fact, taurine 
can be easily crystallized from concentrates of chicken muscle. 
SCHREIER: Dr. Awapara talked about the puzzles of taurine. I should add another puzzle to 
this problem which is that human babies excrete taurine only for about three to six months, 
and prematures do not excrete it until they are about ten to fourteen days old. 
SEGAL: Inrelation to DR. SCHREIER’s comment on the excretion of taurine in the newborn, which 
then ceases, DR. ROSENBERG and I have measured taurine excretion in the Sprague-Dawley rat 
and found that a great deal of the amino nitrogen coming out on the urine daily is in the form of 
taurine. Some years ago there was a very nice report in the analysis of biological fluids by chroma- 
tographic techniques published by the University of Texas. This monograph included a paper 
which showed that there is a marked difference in taurine excretion by various strains of white rats. 
