G. ROBERT GREENBERG 



sion of the |(3-carbon of serine to the formyl group of N^°-formyl- 

 tetrahydrofoHc acid in pig hver extracts, Jaenicke (17) found 

 that he could isolate N^^-hydroxymethyl folic acid from the re- 

 action mixture in addition to the product. A reasonable se- 

 quence of events to be expected was : 



Serine + tetrahydrofolate > 



glycine + N'^-CH20H tetrahydrofolate (1) 



N10-CH2OH tetrahydrofolate + TPN > 



TPNH + Ni«-CHO tetrahydrofolate (2) 



However, in addition an oxidative degradation occurred at 

 such a rate that none of the intermediate accumulated : 



Nio-CH^OH tetrahydrofolate > N'O-CHjOH folate + 4H (3) 



By isolating and characterizing the degradation product he 

 gained insight into the nature of the parent compound. It 

 would be expected that the degradation product was derived from 

 the tetrahydro level compounds. Such a system of course is 

 ideal for fractionation. Initial fractionation was carried out 

 using pigeon liver extract. After fractionation CH20H-tetra- 

 hydrofolate* indeed did accumulate. Pigeon liver has the added 

 advantage that the oxidative degradation reaction is relatively 

 slow in the unfractionated extracts. 



Another example of this type may be taken from the mech- 

 anism of synthesis of the glycinamide ribotide (9,10,15). The 

 sequence of events which is believed to take place is shown below. 



R-5-P + ATP > PRPP + AMP 



PRPP + glutamine * PRA + glutamate + P-P(^2 Pi) 



PRA + glycine + ATP > glycinamide ribotide +? ADP + ?Pi 



R-5-P + 2 ATP + glycine + glutamine 



glycinamide ribotide + glutamate + AMP + ADP + 3 Pi 



It appears that in this system 5-phosphoribosylamine 



* This apparently is one of the compounds found by S. Deodhar and 

 W. Sakami. Private communication. 



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