Abstract
1. 1. tRNA isolated from Ehrlich ascites cells was charged with [ 3H]methionine in the presence of a formyl-group donor and an enzyme extract prepared from an homologous source. Among the deacylation products of the charged tRNA, one component has the same R F value as N- formylmethionine . The radioactivity in the N- formylmethionine region is 5–6% of that in the methionine region. 2. 2. The identity of this compound as an N-substituted derivative of methionine is further supported by the following experiments: (a) at pH 1 it behaves as a neutral molecule and can be more readily extracted with ethyl acetate than methionine, and (b) when attached by an ester linkage to tRNA, it is more resistant to Cu 2+-catalyzed hydrolysis than methionyl-tRNA. 3. 3. When the tRNA was charged with unlabeled methionine, the tRNA preparation could be labeled with [ 3H]formaldehyde but not with [ 14C]acetyl-CoA, indicating that the N-substituted methionine is probably N- formylmethionine .
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