The formation of pyrrolid-2-one-5-carboxylic acid at the N-terminus of immunoglobulin G heavy chain

Stott, D.I. and Munro, A.J. (1972) The formation of pyrrolid-2-one-5-carboxylic acid at the N-terminus of immunoglobulin G heavy chain. Biochemical Journal, 128(5), pp. 1221-1227.

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We propose that pyrrolid-2-one-5-carboxyl-tRNA is not involved in the initiation of protein synthesis in eukaryotic cells and that the <i>N</i>-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 <i>N</i>-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-<sup>14</sup>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 <i>N</i>-termini of the heavy chains.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Stott I, Professor David
Authors: Stott, D.I., and Munro, A.J.
Subjects:Q Science > QR Microbiology > QR180 Immunology
College/School:College of Medical Veterinary and Life Sciences
Journal Name:Biochemical Journal
Journal Abbr.:Biochem j.
Publisher:Portland Press Ltd.
ISSN (Online):1470-8728

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