Haptoglobin. A novel mode of biosynthesis of a liver secretory glycoprotein.
The de novo biosynthesis of the heterotetrameric (alpha 2 beta 2) serum glycoprotein, haptoglobin, was studied using a rabbit reticulocyte cell-free translation system and mRNA preparations from the livers of turpentine-treated rats. Analysis of the translation mixtures with either antisera specific for the alpha-subunit (anti-alpha-IgG) or the beta-subunit (anti-beta-IgG) or the native haptoglobin tetramer (anti-alpha 2 beta 2-IgG) resulted in each instance in the recovery of a single protein exhibiting a Mr = approximately 38,000. Cleavage of the translation product with cyanogen bromide or trypsin resulted in the generation of small peptide fragments that were specifically immunoadsorbed with either anti-alpha-IgG or anti-beta-IgG. These results indicated that the primary translation product of haptoglobin mRNA is a single polypeptide that contains the elements of both the alpha-subunit and the beta-subunit of the protein. Presumably haptoglobin is synthesized in vitro as a single precursor protein that is proteolytically processed post-translationally to form the dissimilar alpha- and beta-subunits of the native protein.
D000818:Animals; D002474:Cell-Free System; D006242:Haptoglobins / Q000096:biosynthesis*; D007249:Inflammation; D008099:Liver / Q000378:metabolism*; D046911:Macromolecular Substances; D008970:Molecular Weight; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D012156:Reticulocytes / Q000378:metabolism
D006242:Haptoglobins; D046911:Macromolecular Substances; D012333:RNA, Messenger