ESMOND E. SNELL > 



nor panthetheine serves as a growth factor; panthetheine- 

 4 '-phosphate (formula XI, an intermediate between pantetheine 

 and coenzyme A) or coenzyme A itself must be supplied to per- 

 mit growth (77a), 



Do conditions exist in which higher animals show similar, 

 synthetic disabilities, where the coenzymes or their more im- 

 mediate (and more readily available) precursors would be more 

 effective therapeutic agents than the vitamin forms of commerce? 

 We do not know. In experimentally produced deficiency states 

 (usually produced in young, undiseased animals) no evidence 

 for this exists, but it would be unwise to overlook the possibility 

 while the problems of pathology of all types, of aging, etc., are 

 still with us. 



When we say that L. bulgaricus has a specific requirement for 

 pantetheine because of an insufficient capacity on the part of 

 the cell to convert pantothenic acid to pantetheine, it is important 

 to understand just what is meant. Experimentally, all that one 

 observes is that to permit growth, pantothenic acid must be 

 supplied in the medium at several hundred times the concentra- 

 tion that suflSces when pantetheine is supplied. But with 

 sufficient pantothenic acid, growth does occur, showing that 

 some of it has been converted to coenzyme A. Thus the con- 

 version enzymes do occur, and can function. Is the conversion 

 limited because (7) insufficient of the conversion enzyme (s) 

 is present, or (2) because the enzyme, though present, has a 

 lowered affinity for its substrate, or {3) because activity of the 



PO3H2 CH3 

 OCH2-CCHOHCONHCH2CH2CONHCH2CH2SH 



CH3 



(XI) Pan tetheine-4' -phosphate 



CHo COOH 



I I 



HOCH2CCHOHCONHCH2CH2CONHCHCH2SH 



CH3 



(XII) Pantothenylcysteine 



98 



