HANS KLENOW 



A more unspecific reaction for nucleotide formation was found by Brawerman and 

 Chargaff (1953). They showed that some unspecific phosphatases have transferase 

 activity also with nucleosides as acceptors. With phenyl phosphate as phosphate 

 donor they found that all possible nucleotides could be formed from the correspond- 

 ing nucleosides in the presence of prostate phosphatase, while a phosphatase from 

 malt under some conditions catalysed the formation of only 5 / -nucleotides. This type 

 of transfer reaction, however, might not play a quantitatively significant role under 

 physiological conditions, at least when growth is involved, as it often requires a high 

 substrate concentration and still gives a fairly low yield. 



An entirely different pathway for nucleotide formation was suggested by some 

 experiments performed with 14 C-labelled formate (Greenberg, 1951). Formic acid is 

 known to be incorporated into the purine ring, and Greenberg was able to isolate 

 labelled hypoxanthine, inosine and inosinic acid from pigeon-liver extracts, which 

 had been incubated with labelled formic acid. But the interesting part of this observa- 

 tion was that the specific activity of inosinic acid was significantly higher than that of 

 inosine and hypoxanthine. In other words, inosine^'-phosphate was probably the 

 primary product, and both the nucleoside and the free base were probably degrada- 

 tion products of the nucleotide. Similarly Leder and Handler (1951), working with 

 nicotinamide nucleotide synthesis in erythrocytes, found evidence for bypassing of 

 the nucleoside stage. Consistent with this concept Buchanan and his group (Williams 

 and Buchanan, 1953) also found evidence for bypassing of inosine in the formation 

 of inosinic acid from hypoxanthine. They furthermore found that synthesis of inosinic 

 acid was considerably activated by addition of ribose-5-phosphate and adenosine 

 triphosphate to pigeon-liver extract. The reaction was shown to be catalysed by at 



Table III 



Reactivation of a dialysed extract of pigeon liver 



■jy — 7,000 counts/min. of 8-carbon-i4-adenine added in every case. 

 (From Saffran, M. and Scarano, E. (1953). Nature, Lond. 172, 949.) 



72 



