Site of synthesis of metallothionein in rat liver.
Free and membrane-attached polysomes were isolated from the liver of normal and cadmium-treated rats, and were translated using L-[35S]cysteine and a nuclease-treated reticulocyte lysate system. The translation products were analyzed for radioactive metallothionein by immunoprecipitation with antibodies to rat cadmium metallothionein followed by sodium dodecyl sulfate--polyacrylamide gel electrophoresis. In both normal and cadmium-treated rats, radioactive metallothionein was produced by free polysomes but not by membrane-attached polysomes. Cadmium treatment did not increase the in vitro ability of polysomes to synthesize metallothionein. As a control, the translation products of these two classes of polysomes were also analyzed for radioactive albumin and it was confirmed that membrane-attached polysomes produce albumin but do not synthesize metallothionein. The cell-free synthesis of metallothionein by free polysomes was also demonstrated by isolation of nascent metallothionein by Sephadex gel filtration and DEAE-cellulose chromatography. In adult rat liver there are two forms of metallothionein and both were produced in vitro by free polysomes.
D000418:Albumins / Q000096:biosynthesis; D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002105:Cadmium Poisoning / Q000378:metabolism*; D008099:Liver; D008297:Male; D008667:Metalloproteins / Q000096:biosynthesis*; D008668:Metallothionein / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects*; D011817:Rabbits; D051381:Rats; D012156:Reticulocytes / Q000378:metabolism
D000418:Albumins; D008667:Metalloproteins; D002104:Cadmium; D008668:Metallothionein