Arginine acid catalytic

Lewis-Acid Catalyzed. Recently, various Lewis acids have been examined as catalyst for the aldol reaction. In the presence of complexes of zinc with aminoesters or aminoalcohols, the dehydration can be avoided and the aldol addition becomes essentially quantitative (Eq. 8.97).245 A microporous coordination polymer obtained by treating anthracene- is (resorcinol) with La(0/Pr)3 possesses catalytic activity for ketone enolization and aldol reactions in pure water at neutral pH.246 The La network is stable against hydrolysis and maintains microporosity and reversible substrate binding that mimicked an enzyme. Zn complexes of proline, lysine, and arginine were found to be efficient catalysts for the aldol addition of p-nitrobenzaldehyde and acetone in an aqueous medium to give quantitative yields and the enantiomeric excesses were up to 56% with 5 mol% of the catalysts at room temperature.247... 

The next question is, where the protons go to in the active site during the catalytic cycle. For the base, there are too many possibilities to be certain. Groups near to the dinuclear cluster that can accept or exchange protons include the side chains of the amino acids arginine and histidine, thiolate ligands to the cluster, and peptide NH groups. 

For example, chymotrypsin cleaves peptides on the C-terminal side of aromatic amino acid residues phenylalanine, tyrosine, and tryptophan, and to a lesser extent some other residues with bulky side-chains, e.g. Leu, Met, Asn, Gin. On the other hand, trypsin cleaves peptides on the C-terminal side of the basic residues arginine and lysine. Elastase usually catalyses hydrolysis of peptide bonds on the C-terminal side of neutral aliphatic amino acids, especially glycine or alanine. These three pancreatic enzymes are about 40% identical in their amino acid sequences, and their catalytic mechanisms are nearly identical. 

Figure 6.2 The mechanism of cytochrome-c-peroxidase complex formation, (a) Native enzyme, (b) Activated complex with the acid-base catalytic function of distal histidine (His) and stabilization of negative charge by arginine (Arg) residue of the active site, (c) Hypothetic intermediate oxene complex, (d) Complex I after intramolecular electron regrouping of oxene complex with Fe4+ and free radical X fragment formation.

Amongst the subnanomolar chymotrypsin inhibitors, modelling of one of the best variants implied a novel inhibitory mechanism for protein serine protease inhibitors, in which two amino acid side chains (arginine and aspartic acid) intrude into the proximity of the catalytic triad of the protease rather than binding in the substrate-binding pockets (see Fig. 4). 

Amino acid and nucleotide sequences of CuZn-SOD have been determined for enzymes from many organisms. The amino acid residues of the metal ligands and the cysteine residues which form disulfide bridge are conserved in all CuZn-SODs so far sequenced. Furthermore, the charged arginine and lysine residues which participate in the catalytic function for attracting anionic O2 to the Cu site are also conserved (Fig. 10.3). The amino... 

Fig. 5.4 Schematic representation of the Poulos-Kraut peroxidase mechanism in which the conserved distal histidine serves as an acid-base catalyst that transfers a proton from the H202 to the terminal oxygen after formation of the [Fe(III)-OOH] intermediate. The proximal histidine iron ligand and the catalytic histidine and arginine are shown. In HRP, these residues are His 170,...

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