BASIC BIOCHEMICAL QUESTIONS 



mission of the code laid down in the genetic material is trans- 

 lated into chemical mechanisms. A chemical methodology of 

 code transmission, it appears, consists of arranging specific 

 sequences through standard links in the line-up. Possibly a 

 master methodology may exist for a specific sequential arrange- 

 ment of unlike units through a common linkage system which 

 forms the backbone structure of the resulting compound. How- 

 ever that may be, patternization or sequential arrangement in- 

 cludes, but largely transcends, what we have been mostly con- 

 cerned with so far, namely, mere mechanisms of linking. 



Synthesis of Peptidic Links 



It has at times appeared that the main problem in under- 

 standing protein synthesis is to tackle the mechanism of peptide 

 bond formation. However, to understand protein synthesis 

 truly, the understanding of peptide bond formation is a premise 

 rather than an end in itself. It will be wise, nevertheless, first 

 to obtain a background by reviewing our present understanding 

 of the mechanism of peptide bond formation. It seems that 

 uniformly, peptide linking starts with the activation of the 

 carboxyi group rather than of the amino group. The primary 

 source of energy appears to be the energy-rich phosphate bonds 

 of ATP, the energy currency. Unfortunately, the finer mech- 

 anism of the conversion of phosphate into active acyl grouping is 

 still only imperfectly understood. There are different subtypes 

 which are of considerable interest. The conversion of phos- 

 phoryl to active acyl may occur (7) by a pyrophosphate elimina- 

 tion from ATP, directly or possibly through other nucleoside 

 triphosphates (NTP) or (2) by phosphorolysis of the terminal 

 phosphate of ATP or other NTP's. These two mechanisms at 

 first looked like interchangeable types of procedure. On close 

 inspection, however, they might represent two distinct and rather 

 different mechanisms. The pyrophosphate elimination, as it 

 seems to develop more and more clearly, leads to a linking be- 

 tween the acyl grouping and die nucleotide part of the NTP (2) 



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