7-Glutamyl peptides hydrolysis

Polymerase Post-glutamyl peptide hydrolysis (PGPH) 398... 

Transpeptidase activity was further studied in extracts of root and sprouting bulbs of Allium cepa. The pH optimum for the hydrolytic activity was 9.0, and it was again concluded that hydrolytic activity was adequate to explain the hydrolysis of y-glutamyl peptides during sprouting of onions. It was confirmed that no enzymatic activity was present in dormant bulbs 8). Subsequently a partially purified enzyme was obtained from sprouted onion bulbs and was shown to have both hydrolytic activity and transpeptidase activity with an optimum pH of 9, although the transpeptidation action was presumably the essential one. The possibility that the crude onion extract also contained a genuine... 

Some y-glutamyl derivatives may be produced by the action of transpeptidase, although the evidence is conflicting (see Section VII. 3.). The production of y-glutamyl peptides in bacterial fermentation broths by reversal of enzymatic hydrolysis has been demonstrated (see Section VII. 3.). Since the concentrations of free amino acids in ripening seeds may attain high values, similar processes may occur in plants. 

My ne. t comments are concerned with the function of the enzymes responsible for the hydrolysis of GSH. We have felt from the start of our work in 1946 that the hydrolysis of GSH is concerned with absorption mechanisms and onlj" indirectly with the synthesis of protein. Thus, we would explain the transpeptidation reactions f rom GSH as a mechanism of transfer of amino acids across cellular membranes. The formation of 7-glutamyl peptides would provide the concentration differential necessary for the absorption of amino acids, for e.xample, from the tubular filtrate or from the intestine. Thus, we would explain the high concentration of the enzymes responsible for transpeptidation in kidney and intestine on the basis that these tissues are the ones most concerned with absorption phenomena. 

Glutamyl endopeptidase [EC 3.4.21.19] (also known as staphylococcal serine proteinase, V8 proteinase, protease V8, and endoproteinase Glu-C), a member of the peptidase family S2B, catalyzes the hydrolysis of Asp-Xaa and Glu-Xaa peptide bonds. In appropriate buffers, the specificity of the bond cleavage is restricted to Glu-Xaa. Peptide bonds involving bulky side chains of hydrophobic aminoacyl residues are hydrolyzed at a lower rate. 

Glutamyl endopeptidase 11 [EC 3.4.21.82], also known as glutamic acid-specific protease, catalyzes the hydrolysis of peptide bonds, exhibiting a preference for Glu-Xaa bonds much more than for Asp-Xaa bonds. The enzyme has a preference for prolyl or leucyl residues at P2 and phenylalanyl at P3. Hydrolysis of Glu-Pro and Asp-Pro bonds is slow. This endopeptidase is a member of the peptidase family S2A. 

Synthetic peptide inhibitors have been developed for a variety of proteases [199-204]. Peptide inhibitors of the metalloprotease angiotensin I converting enzyme (ACE) are of major importance as hypertensive agents [13, 31]. A variety of peptides derived from protease-catalyzed hydrolysis of com cc-zein [202-203] or of wheat germ protein [199, 204] inhibit ACE (Table 6). The most potent of such plant-derived ACE inhibitory peptides is Ile-Val-Tyr (IVY) (Ki 0.1 xM) [199, 204], Further plant-derived peptide ACE inhibitors include the tripeptide glutathione [73, 82], the glutathione -related peptide Y-L-glutamyl-(+)-allyl-L-cysteine sulphoxide [73, 82, 200, 201] and the tripeptide His-His-Leu (HHL) from fermented soybean [201] (Table 6). 

Oxidation of deferrialbomycin S2 with performic acid cleaves the hydroxamic acid linkages and converts the bound NS-hydroxyomithine to glutamic acid, the latter still in peptide combination. Partial acid hydrolysis and identification of fragments affords the structure cyclo-(seryl)s-(glutamyl)3 (135). The oxygen of the side chain of the first serine is linked via sulfur to N1 of 3-methylcytosine, which in turn is acylated with an unknown fragment. 

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). 

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