FREE AMINO ACIDS IN NERVOUS TISSUE 477 
retina is 12.2 wmoles/g (ref. 102). In the fetal mouse’, calf! and human!’, the 
taurine concentration in the brain is higher than in adults. However, there is less 
taurine in tadpole brain than in frog brain™®. The distribution of taurine in parts 
of the human brain has been determined!?’, 
Cystathionine (Table IIA). The occurrence of large amounts of cystathionine in 
human brain, but not in the brains of other animals, except the monkey!™, suggests 
that there may be a metabolic difference between primate brain and the brains of 
other species. The presence of the compound in cerebral cortex taken at biopsy!’, 
the relatively large amount found in monkey brain??? 16, the virtual absence of 
cystathionine in fetal human brains!?’, and the low values found in human cerebellum 
TABLE IIB 
AMINO ACIDS IN NERVE 
Concentrations in yzmoles/g. Reference numbers indicated between ( ). 

Phospho- 





Species Nerve Glycine Alanine Serine Seninie Threonine Taurine 
Hen | Spinal cord | Te? TO 0.81 9 | 0.26, 0.50 | 0.54, 0.84 
| We (USO) ) (256). al (136) ) | (16, 136) | (16, 136) 
Hen | Sciatic 0.56 0.44 0.34 0.20 0.52 
_ herve (136) (136) (136) | (136) | (136) 
Crab | Leg nerve | <5 33 | 65 
| (109) (109) | | (109) 
Lobster | Leg nerve 35 33) ~ 12 
| | (109) (109) (109) 
Cuttlefish _ Axon lee B'S 21 TO 
| | (r09) | (109) | (109) 
Squid | Giant nerve | 11.6, 14.0 | 8.6, 9.0 0, 5-7 | | 2.0 | 76.0, 106.7 
(Loligo pealit) axoplasm _| (46, 96) (46, 96) | (46, 96) | | (46) | (46, 96) 
Squid | Giant nerve | 11.0 OLSee elo 0.32 33-1 
| (46) (46) | (46) | | (46) (46) 
(Dosidicus gigas) | axoplasm 

and other tissues, provide evidence that the high cystathionine content of human 
cerebrum is not a post mortem artifact. (The appreciable amounts of cystathionine 
found in horseshoe-crab brain are a reflection of the fact that almost all of the 
amino acids occur in large amounts in this invertebrate nervel®.) However, the 
cystathionine content of human brain is not consistently high!*’, and the factors 
governing its concentration remain to be elucidated. 
In the rat, a pyridoxine deficiency results in the accumulation of cystathionine 
in the brain and liver; very large amounts (approx. 3.0 wmoles/g) are found in the 
brain®*. The highest concentrations in vitamin B,-deficient rat brain are in the cere- 
bellum (6.7 wmoles/g) and spinal cord (4.7 wmoles/g), decreasing to 1.5 wmoles/g in 
the cerebral hemispheres*?. These findings may have a bearing on the accumulation 
of cystathionine in human brain, though it seems doubtful that the majority of the 
human brain samples could have come from pyridoxine-deficient individuals. 
Furthermore, preliminary experiments by the author have indicated that the cysta- 
thionine content of human cerebellum is low (0.1 wmole/g), in contradistinction to 
the findings in the deficient rat. 
References p. 482/485 
