Degradation by enzymes

Once released, transmitters are inactivated by diffusion into the neighbouring extracellular space, combined with one of two specific pathways either extracellular degradation by enzymes that face the extracellular space, or uptake into cells. 

Since poly(L-tyrosine) cannot be processed into shaped devices, compressed pellets rather than solvent cast films were used as control implants. Poly(L-tyrosine) formed strikingly yellow, moderately inflamed patches that remained at the implantation site throughout the 1-year study. Contrary to soluble proteins or peptides that ar rapidly degraded by enzymes, implants of conventional poly(L-tyro-sine) were evidently nondegradable over a 1-year period. At wee 56 all poly(L-tyrosine) implants were infiltrated by a moderate n ber of inflammatory cells. 

Damaged starch is also more readily degraded by enzymes. The ability to absorb water is the most important property of damaged starch since it adds to the ability of flour to absorb water. If all the starch in a flour is undamaged then only the protein will absorb water. 

Peniche et al. (2004) successfully encapsulated up to 65 % of shark liver oil (rich in polyunsaturated fatty acids) in chitosan/alginate capsules in order to mask the oil s unpleasant taste. Here again it was found that the chitosan coating allowed a greater degree of control of capsule permeability. The capsules could be degraded by enzymes such as lipase or pancreatin. They were initially resistant to the acid environment of the stomach, although after 4 hours under intestinal conditions (pH = 7.4) the capsule walls were finally disrupted. 

Neuropeptides are degraded by enzymes called neutral endopeptidases, which are present adjacent to neuropeptide receptors. Neutral endopeptidases regulate the neuropeptide-induced responses by modulating their levels. Inhibitors of these enzymes are being studied as a potential therapeutic agent for asthmatic disease. In... 

This chapter will discuss some blopharmaceutical aspects of enzyme absorption, although most studies have been performed using other proteins or peptides. Small molecules are predominantly metabolized in the liver, but proteins and peptides are degraded by enzymes present in most compartments of the body. 

The prospects of making pharmacologically more active compounds as well as substances that do not cause dependence by modifying enkephalins, spur the peptide chemist on to greater efforts. As always, the fact that analgesically active peptides are rapidly degraded by enzymes after intracerebroventricular administration in animals represents the main barrier to their therapeutic application. 

Water-soluble polysaccharide species with higher molecular weights can be readily degraded by enzymic hydrolysis with a mixture of pectinase and hemi-cellulase to release the dRG-II complex [45]. The same mixture was found to be efFcient to extract the dRG-II D metal complexes from water-insoluble residues of vegetables, owing to the destruction of the pectic structure [45]. 

Similar results are obtained with degradation by enzymes, but the entire 12% of the starch is converted to degraded amylose and amylopectln. The exact equations for these reactions are not known. 

Pectic substances are important structural components of the middle lamellea and the primary cell walls of higher plants, in particular fruits and vegetables. The extent and mode of their degradation by enzymes affect many aspects of the processing of fruits and vegetables and many quality attributes of fruit and vegetable products. 

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