Peptides enzyme action

In addition to the catalytic action served by the snRNAs in the formation of mRNA, several other enzymatic functions have been attributed to RNA. Ribozymes are RNA molecules with catalytic activity. These generally involve transesterification reactions, and most are concerned with RNA metabofism (spfic-ing and endoribonuclease). Recently, a ribosomal RNA component was noted to hydrolyze an aminoacyl ester and thus to play a central role in peptide bond function (peptidyl transferases see Chapter 38). These observations, made in organelles from plants, yeast, viruses, and higher eukaryotic cells, show that RNA can act as an enzyme. This has revolutionized thinking about enzyme action and the origin of life itself. 

Some active materials are carriers for drugs (drug delivery systems), some have immobilized peptides to enable cell adhesion or migration, some are degradable by hydrolysis or by specific enzyme action. Some contain bioactive agents (e.g., heparin, thrombomodulin) to prevent coagulation or platelet activation while others incorporate bioactive groups to enhance osteo-conduction. Many include polyethylene oxide to retard protein adsorption and this is perhaps the closest we have come to a kind of inertness. 

Therefore, enzyme simulation using short peptides must aim at reproduction of useful functions only. They should not be adjusted to the operation mode of polypeptides (biocatalysts). To put it another way, efforts should be aimed at the synthesis of catalytic biomimics simulating corresponding enzyme action with non-full parameters. It is the author s opinion that this approach will help to resolve the dead-end direction of using peptides as the main construction material. 

Since the fraction was the limit product of enzyme action it was thought to represent a peptide sequence consisting of a small number of amino acid residues lying on either side of the chromophoric nucleus this being so, its molecular size and composition would be fixed by the position of susceptible bonds at each side of the chromophoric residue. Nevertheless, owing to the slowness of the final stages of the enzymatic reaction it was... 

A pro-drug is a substance that has no special biological activity per se but can be converted into an active drug by enzymic action in the body. Thus, all the initial proteins formed by ribosomal synthesis that contain a peptide hormone structure locked within their amino-acid sequence are analogous to pro-drugs. The hormones are released by the action of proteolytic enzymes. Usually, however, the term prodrug is restricted to artificially synthesised molecules that are acted upon by the... 

Solubilization of Protein. Fish protein concentrate has high nutritional quality as determined both from its essential amino acid composition and from animal feeding experiments. Unfortunately, the concentrate is quite insoluble in water because of its denaturation by the solvent extraction method used in processing thus it contributes no functional properties to a food and must be used in bakery products primarily. A potentially useful method of solubilizing the protein is by proteolysis (9-12). As is the case with protein hydrolysates of casein and soybean protein, bitter peptides are formed during the hydrolysis. Papain and ficin produce more of these bitter peptides than does Pronase, for example (12). Pronase was found to produce a more brothy taste (13). A possible method of removing the bitter peptides is to convert the concentrated protein hydrolysate to plastein by further proteolytic enzyme action (14) to remove the bitter peptides. 

It has already been emphasized (p. 14) that the best stage of hydrolysis at which to attempt the fractionation of peptides is at the point where enzyme action will proceed no farther or when there is a very sharp break in the hydrolysis curve. The disadvantage of a long incubation period is of course that the danger of rearrangements increases (see Linder-str0m-Lang and Ottesen, 1949). 

The principles of enzyme action are illustrated by the enzyme chymotrypsin. Chymotrypsin digests proteins in the intestine by hydrolyzing the peptide bond at the carboxy side (to the right as conventionally written) of a hydrophobic amino acid. Thus, the small peptide glycylphenylalanylglycine (GlyPheGly) is hydrolyzed to GlyPhe and Gly. 

Insulin in the body is derived from its precursor molecule proinsulin. During the conversion of proinsulin to insulin, a small peptide (C-peptide) is released by enzymic action. Measurement of this peptide in serum provides a measure of pancreatic -cell function, even in patients on insulin. C-pep-tide determination can be used in the evaluation of a number of metabolic conditions, e.g. brittle diabetes, insulinoma. 

Primosigh, j., Pelzer, H., Maass, D., Weidel, W. Chemical characterization of muco-peptides released from the E. coli B cell wall by enzymic action. Biochim. biophys. Acta (Amst.) 46, 68-80 (196I). 

Chapter 16, Amino Acids, Proteins, and Enzymes, discusses amino acids, formation of peptide bonds and proteins, structural levels of proteins, enzymes, and enzyme action. Amino acids are drawn as their ionized forms in physiological solutions. Section 16.3 describes the primary level of protein structure. Section 16.4 describes the secondary, tertiary, and quaternary levels of proteins. Enzymes are discussed as biological catalysts, along with the impact of inhibitors and dena-turation on enzyme action. 

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