Degradation increased resistance

Ethoxylated andSulfatedAlkylphenols. Because these aLkylphenols degrade less readily than the sulfated alcohol ethoxylates, their anticipated expansion failed to materialize, although by 1965 they were widely used in retail detergent products. Sulfated alkylphenol ethoxylates are used in hospital cleaning products, textile processing, and emulsion polymerization. Sulfated alkyphenol ethoxylates are sold as colorless, odorless aqueous solutions at concentrations of >30%. The presence of ethylene oxide in the molecule increases resistance to hardness ions and reduces skin irritation. Representative commercial sulfated alkylphenol ethoxylates are given in Table 12. 

Pore diameter and distribution are important factors. Small pores limit the accessibihty of internal surface because of increased resistance to diffusion of reactants inwards. Diffusion of products outwards also is slowed, and degradation of those produces may result. 

Increased resistance to degradation during processing or apphcation... 

Replacement of Dha by Dhb and vice versa has been reported for several lantibiotics. Replacement of Ser at position 5 by Thr led to the production of Dhb instead of Dha in mature nisin The mutant exhibited increased resistance to chemical degradation, but this was accompanied by a 2- to 10-fold reduction in bioactivity toward various indicator strains. In contrast, replacement of Dha at position 2 in nisin Z with Dhb resulted in a mutant that was twice as active as native nisin Z. ° The gallidermin variant Dhbl4Dha did not exhibit any noticeable decrease in activity, ° and the DhblODha mutant of mutacin II also showed similar activity as wild type. " The promiscuity of the biosynthetic enzymes is also well illustrated by the production of a nisin mutant with a Dhb residue at position 18 in place of Gly after introduction of a Thr codon in nisA and the analogous introduction of a novel Dha in place of a Lys at position 18 in Pep... 

Armstrong attributed the increased resistance of dentin matrix to proteolysis to the blockage of susceptible sites by covalently bound carbohydrate. Later it became clear that the Maillard reaction induces the formation of covalent bonds (cross-links) between protein molecules, accounting for such resistance as well. The presence of non-degradable matrix proteins inhibits mineral dissolution (Chapter 2). In addition, both brown pigments and cross-linked proteins inhibit the production of extracellular polysaccharides by cariogenic streptococci (Kobayashi et al., 1990). 

That the traits of B. m aterium can be transferred to B. subtilis by plasmid transfer techniques has been established. These traits are increased resistance to naphthalene, parachlorbiphenyl, and dibenzofuran, and increased ability to degrade C-naphthalene. The transformants increased degradative abilities were demonstrated by the accumulation of greater quantitites of water soluble metabolite and the presence of a unique solvent soluble metabolite. 

Functional groups. Halogen substitution to an aromatic compound renders it less degradable. The number of substitutions and the location are important. Chlorophenols are an excellent example of increasing resistance with increasing substimtion. Amino and hydroxyl substitutions often increase degradability. 

Replacement of the amide by a thioamide bond in peptides represents a minimal modification that may be of interest as it increases resistance against enzymatic degradation. 483,484 Such modification has been reported to both increase14 5 486 and decrease biological activities, and the effect is not readily predictable. 487-489 ... 

Pore diameters and their distribution. Small pores limit accessibility of internal surface because of increased resistance to diffusion of reactants inwards. Diffusion of products outward also is slowed down and may result in degradation of those products. When the catalyst is expensive, the inaccessible internal surface is a liability. A more or less uniform pore diameter is desirable, but the distribution usually is statistical and only molecular sieves have nearly uniform pores. Those catalyst granules that are extrudates of compacted masses of smaller particles have tamodal pore size distribution, between the particles and within them. Clearly a compromise between large specific surface and its accessibility as measured by pore diameter is required in some situations. 

It is well known that the incorporation or substitution of a D-tryptophan residue into a biologically active peptide chain enhances the activity of that chain. Furthermore, such incorporation or substitution will prolong the biological activity. The prolonged and enhanced effectiveness of such peptides probably relates the increased resistance to degradation by peptidases. 

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