Alternative proton donors/acceptors in the catalytic mechanism of the glutathione reductase of Escherichia coli: the role of histidine-439 and tyrosine-99

Biochemistry ◽  
1989 ◽  
Vol 28 (25) ◽  
pp. 9602-9607 ◽  
Author(s):  
Mahendra P. Deonarain ◽  
Alan Berry ◽  
Nigel S. Scrutton ◽  
Richard N. Perham
Keyword(s):  
Escherichia Coli ◽  
Glutathione Reductase ◽  
Catalytic Mechanism ◽  
Proton Donors

scholarly journals Phospho-N-Acetyl-Muramyl-Pentapeptide Translocase from Escherichia coli: Catalytic Role of Conserved Aspartic Acid Residues

2004 ◽  
Vol 186 (6) ◽  
pp. 1747-1757 ◽  
Author(s):  
Adrian J. Lloyd ◽  
Philip E. Brandish ◽  
Andrea M. Gilbey ◽  
Timothy D. H. Bugg
Keyword(s):  
Escherichia Coli ◽  
Amino Acid ◽  
Aspartic Acid ◽  
Catalytic Mechanism ◽  
Partial Purification ◽  
Sequence Alignments ◽  
Structural Environment ◽  
Essential Enzyme ◽  
Covalent Intermediate

ABSTRACT Phospho-N-acetyl-muramyl-pentapeptide translocase (translocase 1) catalyzes the first of a sequence of lipid-linked steps that ultimately assemble the peptidoglycan layer of the bacterial cell wall. This essential enzyme is the target of several natural product antibiotics and has recently been the focus of antimicrobial drug discovery programs. The catalytic mechanism of translocase 1 is believed to proceed via a covalent intermediate formed between phospho-N-acetyl-muramyl-pentapeptide and a nucleophilic amino acid residue. Amino acid sequence alignments of the translocase 1 family and members of the related transmembrane phosphosugar transferase superfamily revealed only three conserved residues that possess nucleophilic side chains: the aspartic acid residues D115, D116, and D267. Here we report the expression and partial purification of Escherichia coli translocase 1 as a C-terminal hexahistidine (C-His6) fusion protein. Three enzymes with the site-directed mutations D115N, D116N, and D267N were constructed, expressed, and purified as C-His6 fusions. Enzymatic analysis established that all three mutations eliminated translocase 1 activity, and this finding verified the essential role of these residues. By analogy with the structural environment of the double aspartate motif found in prenyl transferases, we propose a model whereby D115 and D116 chelate a magnesium ion that coordinates with the pyrophosphate bridge of the UDP-N-acetyl-muramyl-pentapeptide substrate and in which D267 therefore fulfills the role of the translocase 1 active-site nucleophile.

scholarly journals Kinetic analysis of the role of lipoic acid residues in the pyruvate dehydrogenase multienzyme complex of Escherichia coli

1980 ◽  
Vol 187 (2) ◽  
pp. 393-401 ◽  
Author(s):  
Mary C. Ambrose-Griffin ◽  
Michael J. Danson ◽  
William G. Griffin ◽  
Geoffrey Hale ◽  
Richard N. Perham
Keyword(s):  
Escherichia Coli ◽  
Lipoic Acid ◽  
Pyruvate Dehydrogenase ◽  
Active Sites ◽  
Catalytic Mechanism ◽  
Pyruvate Dehydrogenase Complex ◽  
Enzymic Activity ◽  
Complex Activity ◽  
Kinetics Of

The catalytic roles of the two reductively acetylatable lipoic acid residues on each lipoate acetyltransferase chain of the pyruvate dehydrogenase complex of Escherichia coli were investigated. Both lipoyl groups are reductively acetylated from pyruvate at the same apparent rate and both can transfer their acetyl groups to CoASH, part-reactions of the overall complex reaction. The complex was treated with N-ethylmaleimide in the presence of pyruvate and the absence of CoASH, conditions that lead to the modification and inactivation of the S-acetyldihydrolipoic acid residues. Modification was found to proceed appreciably faster than the accompanying loss of enzymic activity. The kinetics of the modification were fitted best by supposing that the two lipoyl groups react with the maleimide at different rates, one being modified at approximately 3.5 times the rate of the other. The loss of complex activity took place at a rate approximately equal to that calculated for the modification of the more slowly reacting lipoic acid residue. The simplest interpretation of this result is that only this residue is essential in the overall catalytic mechanism, but an alternative explanation in which one lipoic acid residue can take over the function of another was not ruled out. The kinetics of inactivation could not be reconciled with an obligatory serial interaction between the two lipoic acid residues. Similar experiments with the fluorescent N-[p-(benzimidazol-2-yl)phenyl]maleimide supported these conclusions, although the modification was found to be less specific than with N-ethylmaleimide. The more rapidly modified lipoic acid residue may be involved in the system of intramolecular transacetylation reactions that couple active sites in the lipoate acetyltransferase component.

scholarly journals Escherichia coli alkaline phosphatase. Relaxation spectra of ligand binding

1972 ◽  
Vol 126 (3) ◽  
pp. 727-738 ◽  
Author(s):  
S. E. Halford
Keyword(s):  
Escherichia Coli ◽  
Alkaline Phosphatase ◽  
Ligand Binding ◽  
Catalytic Mechanism ◽  
Temperature Jump ◽  
Relaxation Spectrum ◽  
Equilibrium Mixture ◽  
Difference Spectroscopy ◽  
Relaxation Spectra

The temperature-jump technique was used to study the binding equilibrium between the Escherichia coli alkaline phosphatase dimer and 2-hydroxy-5-nitrobenzyl phosphonate in 0.1m-tris buffer, pH8.0. Three partially discrete relaxations were observed, two of which could be related to the bimolecular associations of ligand with different conformations of the enzyme and the third to the interconversion of these states. Relaxation spectra were also used to analyse the changes in the mechanism of ligand binding to alkaline phosphatase caused by increase in ionic strength. The relaxation spectrum observed after the addition of Pi to the equilibrium mixture of phosphonate and enzyme was also studied. Difference spectroscopy indicated that both of these ligands were bound to the alkaline phosphatase dimer at the same time. These results are related to the catalytic mechanism of this enzyme, with particular reference to the role of two identical subunits in a dimeric enzyme that exhibits only one active site functioning in catalysis at any given time.

scholarly journals The role of His143 in the catalytic mechanism of Escherichia coli aspartate aminotransferase.

1991 ◽  
Vol 266 (10) ◽  
pp. 6079-6085
Author(s):  
T Yano ◽  
S Kuramitsu ◽  
S Tanase ◽  
Y Morino ◽  
K Hiromi ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Aspartate Aminotransferase ◽  
Catalytic Mechanism
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