title: Cell-free synthesis and processing of a putative precursor for mitochondrial carbamyl phosphate synthetase I of rat liver.
abstract: Total RNA or poly(A)(+) RNA of rat liver was translated in a rabbit reticulocyte or wheat germ protein-synthesizing system and the carbamyl phosphate synthetase I [carbamoyl-phosphate synthetase (ammonia); carbon dioxide: ammonia ligase (ADP-forming, carbamate-phosphorylating), EC 6.3.4.16] synthesized was isolated by indirect immunoprecipitation by using antibody purified on enzyme-bound Sepharose and Staphylococcus aureus cells. The in vitro product moved on sodium dodecyl sulfate/polyacrylamide gels as a polypeptide that was about 5000 daltons larger than the subunit of the mature enzyme (160,000 daltons). The same polypeptide was also obtained by direct immunoprecipitation or by a double-antibody precipitation method. The mature enzyme competed effectively with the in vitro product for interaction with anti-carbamyl phosphate synthetase I antibody. Digestion of the in vitro product by S. aureus protease gave a pattern of peptide fragments similar to that of the mature enzyme. A mitochondrial membrane preparation from rat liver converted the in vitro product into a polypeptide that comigrated with the mature subunit on sodium dodecyl sulfate gel electrophoresis. Similar proteolytic activity was not detected in either a cytosol or a microsomal fraction of rat liver. These results indicate that the enzyme is synthesized as a larger precursor which is converted to the mature form of enzyme by posttranslational processing.
mesh_terms: D000818:Animals; D002222:Carbamoyl-Phosphate Synthase (Ammonia) / Q000096:biosynthesis* / Q000302:isolation & purification; D007425:Intracellular Membranes / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology*; D010770:Phosphotransferases / Q000096:biosynthesis*; D010944:Plants / Q000378:metabolism; D011061:Poly A / Q000378:metabolism; D014176:Protein Biosynthesis; D012313:RNA / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D012156:Reticulocytes / Q000378:metabolism; D014908:Triticum / Q000378:metabolism
chemical_list: D011061:Poly A; D012313:RNA; D010770:Phosphotransferases; D002222:Carbamoyl-Phosphate Synthase (Ammonia)