Discrimination significance

Dodd and Johnson14 have shown, however, that the carbanion HNC5H4CH2 does discriminate significantly between various electrophiles (see p. 30). 

Table 5.8 Mean values of CFSV compounds in four Merlot, Teroldego, Marzemino and Chardonnay wines with different aging times. Indexes letters show the variety discrimination significance by Tukey-test.

T7 RNA polymerase incorporates biotinylated nucleotide analogues efficiently (Fenn and Herman, 1990). They noted that this enzyme did not discriminate significantly between UTP and BIO-4-UTP, but its turnover number was reduced from 130 to 28 pmol/min and the from 32 to 77 p.M for UTP and BIO-4-UTP, respectively). T3 RNA polymerase incorporates BIO-ll-UTP most efficiently (3 X SP6 and 2 X T7 RNA polymerase) (D Alessio, 1985). Fenn and Herman (1990) separated the nucleotides obtained after alkaline hydrolysis of the transcripts by reverse-phase HPLC. Gel retardation assays (Theissen et al., 1989) are simpler alternatives (change in mobility of transcripts on polyacrylamide if streptavidin is bound to biotin moieties) although RNA with secondary structures may not allow the streptavidin to bind under native conditions. 

Phosphate modifications T7 polymerase does not discriminate significantly between NTP and [aS] NTP (NEN). To obtain the appropriate modification level the NTP is substituted with [aS] NTP to the desired level. A standard transcription protocol, such as the one described in Section 2.3.1, can be used. 

Figure 10.11 summarizes the measurements for 15 different amino acids. The order of the amino acids is according to their isoelectric points. Interestingly, cyclopeptide 2 is almost not sensitive, whereas the coating with cyclopeptide 1 can discriminate significantly between amino acids of acidic, neutral or basic character. L-Lysine and L-arginine show the strongest interactions, but the response is different between these two amino acids. This strong interaction could be due to direct ionic interactions between amino acid, cyclopeptide 1 and phosphate ions. When we used protected derivatives of lysine and arginine, we were able to confirm that the interaction between 1 and lysine or arginine is mainly dependent on the basic groups of these amino acids (Fig. 10.12). While esterifica-...

Magnetic relaxation studies of this active-site-substituted Cu enzyme indicate that although it is able to bind coenzyme, thereby distorting its metal binding site, it is unable to discriminate significantly between alcohol substrates and water. The restating relatively weak binding of alcohol would explain the lack of catalytic activity for the Cu substituted enzyme. ... 

These problems resisted scientific investigation until the advent of modern biochemical methods. One of the most valuable of these new methods proved to be the use of radiocarbon as a tracer element to follow the newly incorporated carbon dioxide during photosynthesis in a green plant. Photosynthesizing plants do not discriminate significantly between ordinary carbon dioxide, C 02, and radioactive carbon dioxide, C 02. The plants incorporate C 02 into the intermediates in the carbon reduction pathway. 

Porcine liver esterase (PLE) gives excellent enantioselectivity with both dimethyl 3-methylglutarate [19013-37-7] (lb) and malonate (2b) diester. It is apparent from Table 1 that the enzyme s selectivity strongly depends on the size of the alkyl group in the 2-position. The hydrolysis of ethyl derivative (2c) gives the S-enantiomer with 75% ee whereas the hydrolysis of heptyl derivative (2d) results in the R-monoester with 90% ee. Chymotrypsin [9004-07-3] (CT) does not discriminate glutarates that have small substituents in the 3-position well. However, when hydroxyl is replaced by the much bulkier benzyl derivative (Ic), enantioselectivity improves significantly. 

Significant characteristics of homogeneous catalysis are that they are highly specific and proceed under relatively mild conditions— again in contrast to solid catalysis, which is less discriminating as to reaction and may require extremes of temperature and pressure. A problem with homogeneous operation is the difficulty of separating product and catalyst. 

Li+ (0.77) < Na+ (1.0) < K+ (1.48) < Rb+ (1.55) < Cs+ (1.56). While indeed the order is the same, the significant point is that the range of discrimination has been expanded by almost an order of magnitude. The concern then becomes the mechanism whereby the Gramicidin channel effects this enhancement of selectivity. An important source of selectivity that must be considered is the relative solvation energy of water... 

On the discriminating behaviour of metal ions and ligands with regard to their biological significance. H. Sigel and D. B. McCormick, Acc. Chem. Res., 1970,3,201-208 (66). 

Conduritols and inositols are cyclic polyalcohols with significant biological activity. The presence of four stereogenic centers in the stmcture of conduritols allows the existence of 10 stereoisomers. Enzymatic methods have been reported for the resolution of racemic mixtures or the desymmetrization of meso-conduritols. For example, Mucor miehei lipase (MML) showed enantiomeric discrimination between all-(R) and all-(S) stereoisomers ofconduritol E tetraacetate (Figure 6.52). Alcoholysis resulted in the removal of the four acetyl groups ofthe all-(R) enantiomer whereas the all-(S) enantiomer was recovered [141]. 

FIGURE 16.2 Mild-mixing conditions do not discriminate between peptizers (P-44 and R-11) and the control compound. While QDI-containing compounds show significant viscosity reduction. 

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