Enzymatics enzyme degradation

Collagen is the main protein of fhe organic mafrix in denfin and, once demineralized, if is accessible fo profeolyfic enzymes (Klonf ef al., 1991). A number of observafions, however, indicafe fhat carious denfin becomes resisfanf towards enzymatic protein degradation (Young and Massler, 1963). The collagenase-resistant part is rich in carbohydrate... 

Therefore, a combined process of enzymatic protein degradation and resynthesis might be useful in improving both the acceptability and the nutritive values of food proteins at the same time. To carry out the process we have been using in most cases the well-defined proteases, pepsin (EC 3.4.4.1), a-chymotrypsin (EC 3.4.4.5), and papain (EC 3.4.4.10). Our subsequent discussion will therefore center on the three enzymes and their applications to protein degradation and resynthesis. Our use of the word resynthesis refers only to formation of peptide bonds without reference to molecular size of the final product. 

In cells, there is constant synthesis and degradation of enzymes in response to the need for enzymatic activity. Enzyme degradation through proteolysis will often release coenzymes like biotin. Although some biotin molecules can be incorporated into newly synthesized proteins, others are carried by the blood to the kidney, where they are then excreted. Daily excretion of coenzymes leads to a requirement for their replenishment in the diet. 

TRH is synthesized in a wide area of the hypothalamus and is controlled by a non-ribosomal enzyme,TRH-synthetase [31]. It is stored in the median eminence and secreted when required into the hypophysial portal vessels [32]. TRH binds to membrane receptors on the pituitary cells [33] and increases both the synthesis [34] and the release [35] of TSH. Since TRH has been shown to activate adenyl cyclase [36], this action is believed to be mediated via 3, 5 -cyclic adenosine monophosphate (cyclic AMP). The half-life of TRH in vivo is approximately 4 min. It is destroyed in the blood by enzymatic (TRH-degrading enzyme) cleavage of the amide group [37] and excreted via the kidney [32]. The TRH-degrading enzyme is present both in peripheral and hypophysial portal blood of rats but TRH is more rapidly destroyed in the peripheral blood. On the basis of these results, it has been suggested that the portal blood either contains only a low concentration of enzyme or that it contains high concentrations of unidentified substances which act as competitive inhibitors of or substrates for the enzyme [38]. 

Enzyme molecules can easily come into contact with water-soluble substrates, thus allowing the enzymatic reaction to proceed rapidly. The esterase enzyme can hydrolyse polyester chains in PU to diethylene glycol and adipic acid. However, the enzyme molecules are thought to have an extremely inefficient contact with insoluble substrates (e.g., PU). In order to overcome this obstacle, enzymes that degrade insoluble substrates possess some characteristics which allow them to adhere onto the surface of the insoluble substrate [50]. Observations indicate that the polyurethanase PudA enzyme degrades PU in a two-step reaction hydrophobic adsorption onto the PU surface followed by hydrolysis of the ester bonds of PU [9, 50]. 

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