Enzyme-degradable polymers

Enzymes are suitable to break the chains of the thickener directly. Other systems also have been described that enz5rmatically degrade polymers, which degrade into organic acid molecules. These molecules are actually active in the degradation of the thickener [784]. 

As enzymatic oxidative transformation of the PVA polymer can act as a multiple simultaneous event on the polymer with concurrent chain fission by the appropriate enzymes, the polymer can be broken down into small oligomers that can be channelled into the primary metabolism. This picture is not complete because PVA is usually more or less acetylated. The DH is a pivotal factor in almost every aspect of PVA application. Surprisingly there are very few data dealing with the enzymes involved in the deacetylation of not fuUy hydrolysed PVA polymer. In technical processes, esterase enzymes are widely applied to deal with PVAc structures. A good example is from the pulp and paper industry [85], where PVAc, a component of stickies , is hydrolysed to the less sticky PVA. Esterases from natural sources are known to accept the acetyl residues on the polymer as substrate but little detailed knowledge exists about the identity of acetyl esterases in the PVA degradative environment [86]. 

Polynucleotide phosphorylase reversibly forms RNA-like polymers from ribonucleoside 5 -diphosphates, adding or removing ribonucleotides at the 3 -hydroxyl end of the polymer. The enzyme degrades RNA in vivo. 

One of the first examples is a polymer network that consists of polyvinylalco-hol crosslinked by a thrombin-degradable peptide-linker [108] and the encapsulated antibiotic Gentamycin. In the case of a wound infection, the thrombin content increases dramatically. This enzyme degrades the co-network, and releases the Gentamycin, which then fights a possible bacterial infection (see Fig. 7). Suzuki and Tanihara have shown that the antibiotic is only released in the presence of thrombin and only then effectively kills S. aureus and P. aeruginosa cells [109, 110],... 

Multifunctional carrier matrices offer various advantages for oral drug delivery. Their application for oral drug delivery is described in Chapter 8. Generally, such carriers can be used either to protect the drug from enzymatic degradation via steric hindrance or to directly inhibit enzymes. Multifunctional polymers that can inhibit GI proteolytic enzymes per se are polyacrylates and modifications thereof as well as polymer-inhibitor... 

Many different polymers are subject to hydrolysis. Different mechanisms of hydrolysis are usually present in most environments. In contrast to enzymic degradation, where a material is degraded gradually from the surface inwards, chemical hydrolysis of a solid material can take place throughout its cross-section, except for very hydrophobic polymers. 

As a result of the various acidic and enzymic degradative studies on chitin, there can be little doubt that the polysaccharide is a homogeneous polymer composed of 2-acetamido-2-deoxy-D-glucose residues. Moreover, the specificity of chitinases as 2-acetamido-2-deoxy-/3-D-glucosidases confirms the /3-d nature of the glycosidic linkages. 

Wirick MG. Study of the substitution pattern of hydroxyethyl cellulose and its relationship to enzymic degradation. J Polym Set 1968 6(Part A-1) 1705-1718. 

Wirick MG. Study of the enzymic degradation of CMC and other cellulose ethers. / Polym Sci 1968 6(Part A-1) 1965-1974. Anonymous. Final report on the safety assessment of hydroxy-ethylcellulose, hydroxypropylcellulose, methylcellulose, hydroxypropyl methylcellulose and cellulose gum. / Am Coll Toxicol 1986 5(3) 1-60. 

---