Escherichia coli amino acid incorporation enzymes

Remarkably, incorporation of fluorinated amino acids into proteins can also be accomplished in vivo. This supposes that the fluorinated amino acid analogs are recognized by the appropriate amino acyl-tRNA synthetase enzyme with efficiency similar to that of the natural amino acid. The proliferase response elicited by a fluorinated analog (a trifluoroisoleucine derivative) of murine interleukin-2 produced in an appropriate Escherichia coli strain was nearly as high as that of the authentic cytokine, indicating folding into an authentic, native structure [84],... 

The replacement of sulfur-containing amino acids in proteins by their selenium analogs has received some attention. For example, a variant of Escherichia coli was shown to indiscriminately incorporate selenium into its proteins l. In fact, the /8-galactosidase isolated from this system, which had 70-75% of its methionine residues replaced by the selenium analog, exhibited a virtually unaltered catalytic activity. Similarly, the indiscriminate incorporation of selenomethionine in proteins of the rat as well as E. coli suggests that the enzymes methionyl-tRNA synthetase and amino acid polymerase can accept both methionine and selenomethionine and their corresponding tRNA derivatives. There is some evidence which suggests that a similar phenomenon occurs with cysteine and selenocysteine ... 

---