Proteins acid catalysed hydrolysis

Cohen and co-workers combined the unique characteristics of acetyl-dextran (Ac-DEX) and spermine with small interfering RNA - a class of double-stranded RNA molecules, 20-25 base pairs in length - as a delivery system. Ac-DEX possesses several characteristics suitable for the delivery of bioactive agents such as proteins. The novel system combined ease of synthesis and biocompatibility with the advantage of controlled release, i.e., sensitivity to physiologically relevant acidic conditions. Acid-catalysed hydrolysis of spermine-Ac-DEX generated spermine-modified dextran, which could be further metabolised in vivo by enzymes [13]. 

These amino acids form hydrophobic (water-repelling) nonpolar regions in proteins. There are three more of this kind with special roles. Phenylalanine and tryptophan have aromatic rings and, though they are still hydrophobic, they can form attractive 7t-stacking interactions with other aromatic molecules. Enzyme-catalysed hydrolysis of proteins often happens next to one of these residues. Proline is very special. It has its amino group inside a ring and has a different shape from all the other amino acids. It appears in proteins where a bend or a twist in the structure is needed. 

The inactivation of 2-AG in mammals is thought to be mediated by the enzyme monoglyceride lipase (MGL). However, molecular characterisation of MGL was not driven by an interest in 2-AG but by research directed at identification of the enzymes involved in the sequential hydrolysis of stored triglycerides. A mouse cDNA encoding this enzyme was cloned and sequenced by Karlsson et al. (1997) and found to encode a 302 amino acid protein that is expressed in a wide range of tissues, including brain. Subsequently, Dinh et al. (2002) demonstrated that rat MGL catalyses hydrolysis of 2-AG when expressed in cells. Interestingly, 2-AG is... 

Pspsin (EC 3.4.23.1) a protease in the stomach of all vertebrates with the exception of stomachless fish (e.g. carp). Purified P. shows maximal activity at pH 1-2, but in the stomach the optimal pH is 2-4. Above pH 6, P. is inactivated by denaturation. It preferentially catalyses hydrolysis of peptide bonds between two hydrophobic amino acids (Phe-Leu, Phe-Phe, Phe-TyrT With the exception of protamines, keratin, mucin, ovomucoid and other carbohydrate-rich proteins, most proteins are attacked by P. The products of P. action are peptone, i. e. mixtures of peptides in the M range 300-3,000. P. is a highly acidic (pi 1), single chain phosphoprotein (327 amino acid residues of known primary sequence, M, 34,500), which is released from its zymogen (pepsinogen, 42,500) by autocatalysis in the presence of hydrochloric acid. 

Protein solutions should not be stored at a pH which is equal to their iso-electric point. At the iso-electric point, the amount of deprotonated carboxylic acid groups and protonated amino groups are equal and thus the net charge of the particle is zero. In that situation the zeta-potential is zero and irreversible aggregation can easily occur. For the same reason, the electrolyte concentration in the solution should not be too high. A very low or high pH is not recommended because the hydrolysis of proteins is both acid and base catalysed. The oxidation of many proteins is catalysed by the divalent metal ions, in particular Fe and Cu ". Divalent metal ion catalysed oxidation of proteins can be prevented by the addition of disodium edetate to complex these ions. However, certain divalent metal ions can also act as stabilisers for specific proteins. 

The human organism is not able to use dietary proteins as such. They must be hydrolysed into single amino acid molecules before they can be absorbed. The hydrolysis of proteins (mostly denatured proteins) is catalysed by proteolytic enzymes called proteases (proteinases or peptidases), which have relatively high substrate specificity. They catalyse the hydrolysis of interior peptide bonds to form peptides of different sizes (endopeptidases such as pepsin, trypsin and chymotrypsin) or attack the terminal amino acids (exopeptidases). Hydrolysis of the N-terminal amino acids is... 

Peptidases are enzymes that catalyse the hydrolysis of peptide bonds - the bonds between amino acids that are found in peptides and proteins. The terms protease , proteinase and proteolytic enzyme are synonymous, but strictly speaking can only be applied to peptidases that hydrolase bonds in proteins. Because there are many peptidases that act only on peptides, the term peptidase is recommended. Peptidases are included in subclass 3.4 of enzyme nomenclature [1,5]. 

Chymotrypein is a proteolytic and milk-curdling enzyme of the pancreatic secretion. It is a protein endopeptidase which catalyses the hydrolysis of native proteins to peptones, polypeptides and amino acids, by breaking the peptide linkages of the carboxyl groups of tyrosine and phenylalanine. 

A semi-synthetic metalloenzyme that catalyses the enantioselective hydrolysis of simple amino acid esters has been reported. Iodoacetamido-l,10-phenanthroline (238) was interacted with a cysteine residue in adipocyte lipid binding protein (ALBP) to produce the conjugate ALBP-Phen (239), which was converted into its Cu(II) complex. The ALBP-Phen-Cu(II) was found to catalyse the enantioselective... 

Protein digestion occurs in two stages endopeptidases catalyse the hydrolysis of peptide bonds within the protein molecule to form peptides, and the peptides are hydrolysed to form the amino acids by exopeptidases and dipeptidases. Enteropeptidase initiates pro-enzyme activation in the small intestine by catalysing the conversion of trypsinogen into trypsin. Trypsin is able to achieve further activation of trypsinogen, i.e. an autocatalytic process, and also activates chymotrypsinogen and pro-elastase, by the selective hydro-... 

A solution to this problem was proposed in the 1960s by Sidney Fox, on the basis of experimental results that he obtained by heating up a mixture of amino acids in the absence of water. Fox found that, in these conditions, amino acids do aggregate into macromolecules which can even reach large dimensions, and which he called proteinoids. These are not real proteins because their amino acids are not arranged in linear chains of polypeptides, but form directly a variety of three-dimensional chemical bonds. Proteinoids, however, are somewhat similar to proteins in various respects, including a weak catalytic activity (they can, for example, catalyse ATP hydrolysis). 

There are 48 structural and cross-linking amino acids concerned with the shape of the protein but over half of the amino adds have functional groups sticking out of the chain—amino, hydroxy, acid groups, and the like. In fact, the enzyme uses only a few of these functional groups in the reaction it catalyses (the hydrolysis of RNA)—probably only two histidines and one lysine—but it is typical of enzymes that they have a vast array of functional groups available for chemical reactions. 

Plants also produce structurally related enzymes (chitinases) that catalyse the hydrolysis of chitin (Table 12.2) and hence damage chitin-based insect integuments. Class I chitinases are basic enzymes with an jV-terminal hevein-related CBD and vacuole-targeting C-terminal signals whereas Class II enzymes are acidic proteins lacking these CBD and vacuole-targeting domains. Class IV chitinases are variously basic and acidic extracellular proteins with... 

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