Lysine function

Fig. 8 Endothelialization on PEU surfaces modified by MPEO-derived SMAs. A Un-treated PEU surface (control) imaged by optical microscopy [OM] B MPEO-OH (without functional endgroups at the end of PEG spacers) as SMA imaged by scanning electronic microscopy [SEM] basic amino acid (typically lysine)-functionalized MPEO derivatives as SMA by C OM and D SEM arginine-glycin-aspartic acid tri-peptide sequence [RGD]-functionalized MPEO derivatives as SMA by E OM and F SEM [82,83]. Reproduced from [180,181]...

The most commonly used method to exploit silica for gene delivery is by functionalizing the surface of the NPs with aminosi-lanes (either N-(2-aminoethyl)-3-aminopropyltrimethoxysilane or N-(6-aminohexyl)- 3-aminopropyltrimethoxysilane). The group of Lehr showed that commercially available silica NPs functionalized with N-(6-aminohexyl)- 3-aminopropyltrimethoxysilane were able to transfect efficiently Cos-1 cells with very low toxicity. Other cationic silica nanoparticles with surfaces modified by amino-hexyl-aminopropyltri- methoxysilane (AHAPS) were also reported recently to be successful transfection reagents. He et al used a similar approach but they directly synthesised positively charged amino-modified silica NPs. They showed that these NPs were able to protect pDNA from DNasel degradation in vitro in Cos-7 cells, thus evidencing a simple and efficient protection method. Zhu et also showed the successful delivery of antisense ODN with poly(L-lysine) functionalized silica nanoparticles in HNEI and HeLa cells. 

L-Lysine is an indispensable dibasic AA (L-2,6-diaminohexanoic add) required for hiunan growth and for maintaining nitrogen balance in adults. Lysine cannot be synthesized by the body, and therefore must be supplied through diet. Lysine and threonine are the only essential AAs whose amino gronps do not contiibnte to the total body amino pool because they do not participate in transamination reactions. Metabolites of lysine catabolism enter the TCA cycle only at the acetyl-CoA site, and therefore cannot serve as substrates for glucose synthesis. Consequently, lysine functions strictly as a ketogenic AA. ... 

Leonard, J.K., Hopkins, T.E., Chaffin, K., and Wagener, K.B. (2008) SemicrystaUine lysine functionalized precision polyolefins. Macromolecular Chemistry and Physics, 209,1485-1494. 

Another biomedical appHcation of mictocapsules is the encapsulation of Hve mammalian ceUs for transplantation into humans. The purpose of encapsulation is to protect the transplanted ceUs or organisms from rejection by the host. The capsule sheU must prevent entrance of harmful agents into the capsule, aUow free transport of nutrients necessary for ceU functioning into the capsule, and aUow desirable ceUular products to freely escape from the capsule. This type of encapsulation has been carried out with a number of different types of Hve ceUs, but studies with encapsulated pancreatic islets or islets of Langerhans ate most common. The alginate—poly(L-lysine) encapsulation process originally developed in 1981 (54) catalyzed much of the ceU encapsulation work carried out since. A discussion of the obstacles to the appHcation of microencapsulation in islet transplantation reviewed much of the mote recent work done in this area (55). Animal ceU encapsulation has also been researched (56). 

Reaction with Phosgene. This reaction of amino acid esters is used for preparing the corresponding isocyanates, especially lysine diisocyanate [4460-02-0] (LDI). LDI is a valuable nonyellowing isocyanate with a functional side group for incorporation in polyurethanes. 

Biochemical Functions. Ascorbic acid has various biochemical functions, involving, for example, coUagen synthesis, immune function, dmg metabohsm, folate metaboHsm, cholesterol cataboHsm, iron metaboHsm, and carnitine biosynthesis. Clear-cut evidence for its biochemical role is available only with respect to coUagen biosynthesis (hydroxylation of prolin and lysine). In addition, ascorbic acid can act as a reducing agent and as an effective antioxidant. Ascorbic acid also interferes with nitrosamine formation by reacting direcdy with nitrites, and consequently may potentially reduce cancer risk. 

Heterocyclic enamines A -pyrroline and A -piperideine are the precursors of compounds containing the pyrrolidine or piperidine rings in the molecule. Such compounds and their N-methylated analogs are believed to originate from arginine and lysine (291) by metabolic conversion. Under cellular conditions the proper reaction with an active methylene compound proceeds via an aldehyde ammonia, which is in equilibrium with other possible tautomeric forms. It is necessary to admit the involvement of the corresponding a-ketoacid (12,292) instead of an enamine. The a-ketoacid constitutes an intermediate state in the degradation of an amino acid to an aldehyde. a-Ketoacids or suitably substituted aromatic compounds may function as components in active methylene reactions (Scheme 17). 

FIGURE 5.20 Trypsin is a proteolytic enzyme, or protease, that specifically cleaves only those peptide bonds in which arginine or lysine contributes the carbonyl function. The products of the reaction are a mixture of peptide fragments with C-terminal Arg or Lys residues and a single peptide derived from the polypeptide s C-terminal end. 

FIGURE 18.32 Biotin is covalently linked to a protein via the e-amino group of a lysine residue. The biotin ring is thus tethered to the protein by a 10-atom chain. It functions by carrying carboxyl groups between distant sites on biotin-dependent enzymes. 

The transaldolase functions primarily to make a useful glycolytic substrate from the sedoheptulose-7-phosphate produced by the first transketolase reaction. This reaction (Figure 23.35) is quite similar to the aldolase reaction of glycolysis, involving formation of a Schiff base intermediate between the sedohep-tulose-7-phosphate and an active-site lysine residue (Figure 23.36). Elimination of the erythrose-4-phosphate product leaves an enamine of dihydroxyacetone, which remains stable at the active site (without imine hydrolysis) until the other substrate comes into position. Attack of the enamine carbanion at the carbonyl carbon of glyceraldehyde-3-phosphate is followed by hydrolysis of the Schiff base (imine) to yield the product fructose-6-phosphate. 

The 20 common amino acids can be further classified as neutral, acidic, or basic, depending on the structure of their side chains. Fifteen of the twenty have neutral side chains, two (aspartic acid and glutamic acid) have an extra carboxylic acid function in their side chains, and three (lysine, arginine, and histidine) have basic amino groups in their side chains. Note that both cysteine (a thiol) and tyrosine (a phenol), although usually classified as neutral amino acids, nevertheless have weakly acidic side chains that can be deprotonated in strongly basic solution. 

Ubiquitin/Proteasome. Figure 2 Functional consequences of ubiquitin linkage. Substrates (blue bars) are linked via lysine residues (K) to ubiquitin or ubiquitin chains, (a) Attachment of chains connected via Lysines in position 48 of ubiquitin (K48) targets substrates for proteasomal degradation. In contrast modification of one (b) or multiple (c) lysines by a single ubiquitin molecule mediates novel protein interactions or initiates endocytosis. Conjugation of K63-linked polyubiquitin (d) alters protein function and can also serve as a signal for endocytosis. 

On the whole, curing procedures appear a promising way to obtain very stable polymer films. Thus, the structure of already mentioned polylysine has been revised as a block polymer involving either the a or e amino groups of lysine Vitamin Bj2 modified carbon electrodes were prepared by thermal curing of a mixture of a diamino functionalized derivative 5 and an epoxy prepolymer 6 of the araldite... 

Chattaraj PK, Parr RG (1993) Density Functional Theory of Chemical Hardness. 80 11-26 Cheh AM, Neilands JP (1976) The j -Aminoevulinate Dehydratases Molecular and Environmental Properties. 29 123-169 Chimiak A, Neilands JB (1984) Lysine Analogues of Siderophores. 58 89-96 Christensen JJ, see Izatt RM (1973) 16 161-189... 

Besides all the sensory and texturizing properties, GA has interesting antioxidant properties such as an efficient capacity for deactivation of excited electronic states and moderated radical scavenging capacity. There is increasing experimental evidence that associate the antioxidant function with its protein fraction, mainly by amino acid residues such as histidine, tyrosine and lysine, which are generally considered as antioxidants molecules (Marcuse, 1960,1962 Park et al., 2005). 

Note The amino acid residues of lysine (K) and arginine (R) which may be responsible for the binding of POs to polysaccharides are in bold. According to Demand et al. (2002), the mutual substitution of these amino acids has no influence on the sorption properties of the ATg08770 PO of Arabidopsis with pectins, and the deletion of the fragment results in the loss of this function. 

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