title: Studies on rat liver catalase. IX. Role of methionine in polypeptide chain inhibition.
abstract: Initiation with methionine of the synthesis of rat liver catalase [EC 1.11.1.6] has been investigated. Analysis of the N-terminal residue of nascent catalase peptides labeled in vivo with injected radioactive amino acids, including [3H]methionine, indicated a remarkably high content of methionine. By fractionating [3H]methionine-labeled nascent catalase according to chain length, it was found that peptides of shorter chain length contained more N-terminal methionine relative to total methionine incorporated. In addition, only a small amount of [3H]methionine was detected as the N-terminal amino acid when newly completed catalase was examined by Edman degradation. These results indicate that the synthesis of liver catalase is initiated with methionine, and suggest the presence of a mechanism for its subsequent removal from the N-terminal position. Catalase was also synthesized in a cell-free system directed by the catalase mRNA, using [3H]Met-tRNAf or [3H]Met-tRNAm. The results obtained in such in vitro experiments were in good agreement with those from in vivo studies, and further showed that the N-terminal methionine was provided by a specific initiator tRNA, i.e. tRNA Met f.
mesh_terms: D000818:Animals; D002374:Catalase / Q000096:biosynthesis*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008715:Methionine / Q000378:metabolism*; D010442:Peptide Chain Initiation, Translational; D011132:Polyribosomes / Q000201:enzymology; D012343:RNA, Transfer / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D012270:Ribosomes / Q000201:enzymology
chemical_list: D012343:RNA, Transfer; D008715:Methionine; D002374:Catalase