Pyrrolidone carboxylic acid residue

Recently, the reduction of an N-terminal pyrrolidone carboxylic acid residue of proteins with diborane in tetrahydrofuran or tetramethyl urea was attempted with some success the N-terminal pyrrolidone carboxylic acid residue may thus be identified by its conversion to proline... 

Special procedures (44) are required for the demonstration of N-terminal pyrrolidone carboxylic acid residues in peptides and proteins frequently, pyrrolidone carboxylyl-peptides can be detected by the procedure of Rydon and Smith (SO). Discovery of enzymes capable of cleaving pyrrolidone carboxylic acid from the N-terminus of peptide chains should facilitate studies of this type (45, 46) (see below). 

A cyclic, internal amide derivative of glutamic acid is pyrrolidone carboxylic acid (also known as pyroglu-tamic acid or 2-oxoproline). Some proteins (e.g., heavy chains of immunoglobulins Chapter 35) and peptides (e.g., thyrotropin-releasing hormone Chapter 33) have py-roglutamic acid as their N-terminal amino acid residue. 

Pyrrolidone carboxylic acid is the N-terminal amino acid residue of the /3-chain of fibrinogen from several species (229,230,242). The amino acid sequence containing pyrrolidone carboxylic acid (Glu) is (243) ... 

The N-terminal residue of the al and < 2 chains of collagen is pyrrolidone carboxylic acid (231). Action of procollagen peptidase on... 

Syntheses for all but the feline peptide have been reported. All are 17-residue peptides having the amino end blocked by a pyrrolidone carboxylic acid (PCA, pyroglutamic acid) residue, and the carboxyl group blocked as the amide. The structures of these peptides, which differ by no more than two amino acids, are shown below K... 

Figure 1.3 Amino acid sequences of human V region subgroups. A straight line indicates that a residue is identical to that in the first sequence listed for that subgroup. ( ) Empty parentheses are gaps inserted to maximize homologies. (-) Undetermined amino acid residues. PCA, pyrrolidone carboxylic acid. Protein O/u has an insertion of four Tyr in a row at position 110. Patient Til had a biclonal gammopathy (IgG2, IgM). Both proteins appear to have the same V sequence (refs. 8-22).

The numbers, 216, 231 and 252, over the residues indicate the position corresponding to the sequence of y H chain . PCA pyrrolidone carboxylic acid. 

The hydrolysate is subsequently neutralized to pH 5.8 with sodium or calcium carbonate or with sodium hydroxide solution. In this process, the pH range of 2.5-4 must be passed through as quickly as possible to repress the formation of pyrrolidone carboxylic acid from glutamic acid. The hydroysate is filtered and the filtrate (seasoning) stored. The filtration residue is washed with water and refiltered, if necessary. The diluted filtrate is evaporated and added to the seasoning obtained in the first step. 

This was first foimd by Sanger et al. (1955) in a peptide from insulin and was observed with other peptides by Hirs et al. (1956) and Smyth et al. (1962). The reaction appears to occur when acidic buffers or dilute acids are employed for isolation of peptides. Conversion of the cyclic pyrrolidone carboxyl residue to a glutamyl residue is obtained on mild hydrolysis in dilute acids or alkalies. The cyclization reaction leads to difficulties when sequence methods are used which proceed from the amino-terminal end of a peptide. In addition, this reaction can occur when an internal glutamine residue becomes amino-terminal in the course of stepwise sequence analysis under acidic conditions, as in the Edman methods. An incorrect sequence for a peptide from ribonuclease was deduced as the result of cyclization of amino-terminal glutamine and acidic destruction of serine and threonine in the same peptide (Smyth et al., 1962). 

Proline iminopeptidase [L-Prolylpeptide hydrolase] (3.4.11.5) is produced. [Formerly EC3.4.1.4.] Pyroglutamyl aminopeptidase [L-Pyroglutamyl-peptide hydrolase, Pyrrolidone-carboxylate peptidase] (3.4.11.8) is produced. [Removes pyroglutamate from various penultimate amino acid residues except L-proline. Occurs in Pseudomonas, Bacillus subtilis, rat liver.]... 

Among recent references to cationic polymerization in the presence of carbon black is the report of a graft polymerization of poly(lV-vinyl-2-pyrrolidone) (NVP) onto a carbon black substrate. Typical carbon black surface structures include carboxylic acid groups. From the dependence of polymerization rate on the concentration of these groups and the effects of surface treatments with basic compounds the inference is drawn that the carboxylic acids initiate cationic polymerizations. In the case of NVP grafting the mechanism would presumably involve proton initiation followed by termination on the residual anionic surface groups. 

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