Environment Enzymatic attacks

Self-assembly of phospholipids, such as phosphatidylcholine, a nutritional supplement, in the presence of calcium creates 50-500 nm large, continuous, solid, lipid bilayer sheets rolled into a spiral structure termed nanocochleates.f These can be made to envelope a lipid-soluble drug, such as amphotericin B, to exclude water and protect against pH, oxidation, light, enzymatic attack, hydrolysis, and extremes in temperature. The nanocochleates will convert to liposomes at a pH greater than 6.5 in a calcium deficient environment as is found in the cell (typically less than 1-2... 

As the discussion above implies, there are several different types of enzymatic attack on solid polymers. The simplest case in concept is attack on the polymer by a soluble, freely diffusing, extracellular enzyme which degrades the polymer to form water soluble, low molecular weight fragments that dissolve and diffuse through the aqueous environment until they are taken up by the microorganisms that produced and secreted the depolymerase enzyme. A more complex case is that in which the enzyme is associated with or bound to the outer wall or cell surface of the microorganism, which must attach itself to the polymer surface to permit the immobilized enzyme to seek out the section of the polymer... 

According to literature, degradation of aliphatic polyesters in a living environment can result from enzymatic attack or from simple hydrolysis of ester bonds or both. 

The natural polymers derived from various vegetable and natural tissues are highly diversified either in composition or behavior. In its turn, biodegradation is promoted by enzymes and may be aerobic or anaerobic. Operating in all environments burial in soil, surface exposure, water immersion, in vivo, etc., enzymatic attack may lead to the complete removal of the products from the environment. 

All the transformations carried out with penicillin acylase and employing phenylacetates or -amides as substrates are hampered by the very limited solubility of these esters in aqueous environments. Although the enzyme tolerates considerable amounts of organic cosolvents, generally their application results in at least a partial deactivation of the enzyme. Since penicillin acylase accepts variations in the phenylacetic acid part of its substrates, pyridyl acetic acid esters were employed to enhance the solubihty of the substrates in aqueous solution. In fact, several simple 4-pyridylacetates turned out to be fairly soluble in aqueous media and were attacked at very acceptable rates by the enzyme [ 19 ]. It is interesting to note that the velocity of the enzymatic transformations depends... 

In contrast to the cellular environment, where enzymatic degradation of proteins is highly controlled, extracellular proteases are the cause of uncontrolled protein degradation. The result of this proteolytic attack may vary from complete hydrolysis, single breaks within the peptide chain, or loss of a few N- or C-terminal amino acid residues. Besides losing the product, presence of truncated forms may seriously challenge the purification design. 

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