title: The formation of pyrrolid-2-one-5-carboxylic acid at the N-terminus of immunoglobulin G heavy chain.
abstract: We propose that pyrrolid-2-one-5-carboxyl-tRNA is not involved in the initiation of protein synthesis in eukaryotic cells and that the N-terminal pyrrolid-2-one-5-carboxylic acid group of an IgG (immunoglobulin G) (that secreted by the mouse plasmacytoma Adj PC5) is formed by the enzymic cyclization of the N-terminal glutamine of the heavy chain of the completed IgG molecule and that the cyclization takes place inside the cell. We base these conclusions on the following evidence. (1) Pyrrolidonecarboxyl-tRNA was not found in incorporation experiments with rat liver preparations and [U-(14)C]-pyrrolidonecarboxylic acid, glutamic acid and glutamine, even though an incorporation extent of less than 2% of the total products could have been detected. (2) Double-labelling experiments showed that less than 8% of the nascent peptides of heavy chains (those obtained by precipitation by the antibody to Fc fragment) began with pyrrolidonecarboxylic acid. (3) Further double-labelling experiments showed that 60-66% of the heavy chains of the completed intracellular IgG molecule began with pyrrolidonecarboxylic acid after both 1 and 5h of labelling. (4) The IgG, after secretion by plasmacytoma Adj PC5, was found to have the sequence [unk]Glu- Val-Gln-Leu- at the N-termini of the heavy chains.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000096:biosynthesis*; D000818:Animals; D002247:Carbon Isotopes; D005973:Glutamine / Q000378:metabolism; D007141:Immunoglobulin Fc Fragments; D007128:Immunoglobulin Fragments / Q000096:biosynthesis*; D007074:Immunoglobulin G / Q000096:biosynthesis*; D008099:Liver / Q000378:metabolism; D051379:Mice; D010954:Plasmacytoma / Q000378:metabolism; D011760:Pyrrolidinones / Q000096:biosynthesis*; D011761:Pyrrolidonecarboxylic Acid / Q000096:biosynthesis / Q000378:metabolism; D012343:RNA, Transfer; D014316:Tritium; D014633:Valine / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D007141:Immunoglobulin Fc Fragments; D007128:Immunoglobulin Fragments; D007074:Immunoglobulin G; D011760:Pyrrolidinones; D005973:Glutamine; D014316:Tritium; D012343:RNA, Transfer; D014633:Valine; D011761:Pyrrolidonecarboxylic Acid