Peptidase 7-glutamyl

Figure 544 Proposed camalexin biosynthetic pathway in Arabidopsis. Trp, tryptophan lAOx, indole-3-acetaldoxime IAN, indole-3-acetonitrile DHCA, dihydrocamalexic acid. Enzymes CYP79B2, CYP79B3, CYP71A13, CYP71B15, cytochrome P450 monooxygenases GSTF6, glutathione 5-transferase GGPl, y-glutamyl peptidase.

Austin, S. J., and S. Schwimmer L-y-Glutamyl peptidase activity in sprouted onion. Enzymologia 40, 273 (1971). 

This enzyme [EC 3.4.19.5], now known as /3-aspartyl-peptidase, is a mammahan cytosolic protein that catalyzes the hydrolysis of a /3-hnked aspartyl residue from the N-terminus of a polypeptide. Other isopeptide linkages (e.g., a y-glutamyl hnkage) are not hydrolyzed by this enzyme. 

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. 

Probably the most important protective mechanisms involve the tripeptide GSH (chap. 4, Fig. 59). This compound is found in most cells, and in liver cells, it occurs at a relatively high concentration, about 5 mM or more. There are three pools of GSH cytosolic, mitochondrial, and nuclear. GSH structure is unusual for a peptide in the glutamyl, and cysteine residues are not coupled via a peptide bond, hence the molecule is resistance to peptidase attack. It has a nucleophilic thiol group, and it can detoxify substances in one of three ways ... 

Fig. 1. The y-glutamyl cycle. I, y-Glutamylcysteine synthetase II, glutathione synthetase III, y-glutamyl transpeptidase IV, y-glutamyl cyclotransferase V. peptidase. PCA = pyrrolidone carboxylic acid AA = amino acid.

Once formed, GSH conjugates may be excreted as such (they are best characterized in vitro or in the bile of laboratory animals), bnt they usually undergo fnrther biotransformation prior to nrinary or fecal excretion. Cleavage of the glutamyl and cysteinyl residues by peptidases leave a cysteine conjn-gate, which is fnrther N-acetylated by cysteine-5-conjugate A-acetyltransferase (EC 2.3.1.80) to yield an A-acetylcysteine... 

Lex A repressor), S26 (signal peptidase I), S41 (TSP protease), and S44 (tricorn protease). All known members of clan SH (catalytic triad His, Ser, His) are endopeptidases from DNA viruses which are involved in virus prohead assembly. The clan includes only the family S21 (Cytomegalovirus assemblin). Clan TA with the catalytic residue Thr, Ser or Cys, and an a,(3,a,p sandwich fold includes a number of peptidases whose only proteolytic activity is self-activation. Important families of this clan are T1 (proteasome), and S42 (y-glutamyl transpeptidase). 

Stoykova, S., C. Philippon, F. Labaille, D. Prevot, and Y. Manuel. 1983. Comparative study of alanine-amino-peptidase and gamma-glutamyl-transferase activity in normal Wistar rat urine. Laboratory Animals 17 246-251. 

Brush-border membrane alkaline phosphatase (EC 3.1.3.1) of the rat small intestine was inactivated in an in vitro Fe /ascorbate oxygen-radical generating system (Dudeja and Brasitus 1993). The activities of sucrase, maltase, leucine amino-peptidase, and y-glutamyl transpeptidase were unchanged. 

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