216 R. G. WESTALL 
the condensation of citrulline and aspartic acid in the presence of ATP and an enzyme 
present in liver tissue. It can also be prepared similarly by the action of arginino- 
succinase (ASase), which will reverse its usual action if the substrate is loaded with 
arginine and fumaric acid* 8°. RATNER ef al.84 found ASase activity in liver and 
kidney and lately WALKER*® has found similar activity in a number of other body 
organs including the brain. 
We can only speculate, at this stage, as to where the metabolic block in this disease 


CYSTA 
Fig. 17. A paper chromatogram of the urine of the only known case of cystathioninuria. 
might be found. The most obvious site would be at the point of breakdown of ASA 
into arginine and fumaric acid and this reaction is catalysed by the enzyme ASase. 
We have recently been able to show that ASase is present in normal red blood cells. 
On testing the red cells of the affected children we found that the ASase activity 
was reduced to one-fifth or less’’. If this lowered activity in the red cells reflects a 
similar condition in the other cells in the body where ASA is being synthesized then 
it is likely that ASA will accumulate, flood out of the cells into the extracellular system 
and be excreted in the urine. If there was no ASase at all in their tissues it is difficult 
to see how they could make urea, as in fact they do. Perhaps in such a large organ as 
References p. 217/219 
