Modifications, group-specific

Group-specific modifications of Cb5R have shown similarly that a tyrosine participates in FAD binding (Strittmatter, 1961). Two tyrosines are conserved (Tyr719 and Tyr757 in tobacco) both of which lie in the N-terminal half of the FAD domain. 

An alternative to modifying the functional group attached to fibrils is to utilise the chemistry present in the amino acid side chains. Furthermore, as peptides often undergo specific modification by enzymes in vivo, these could be harnessed for synthetic purposes. Qll (Ac-QQKFQFQFEQQ-Am, a fibril-forming peptide based on Pi 1-2), was coupled to lysine-based molecules by treatment with an enzyme (tissue transglutaminase, TGase) which results in a reaction between lysine and glutamine side chains [72] (Fig. 32). 

There are many ligands and group-specific reagents that have been demonstrated to alter the properties of H,K-ATPase, and which are not clinically useful. For example, there is a variety of chemicals that have been used in studies on structure-function relations of H,K-ATPase and that inhibit the enzyme in vitro by modification of its amino [49,67,158], sulfhydryl [95,165,166] or carboxyl groups [140]. 

Figure 2.7. Identification ofphosphoproteins by site-specific chemical modification. A. Method of Zhou et al. (2001) involves trypsin digest of complex protein mixture followed by addition of sulfhydryl groups specifically to phosphopeptides. The sulfhydryl group allows capture of the peptide on a bead. Elution of the peptides restores the phosphate and the resulting phosphopeptide is analyzed by tandem mass spectrometry. B. Method of creates a biotin tag in place of the phosphate group. The biotin tag is used for subsequent affinity purification. The purified proteins are proteolyzed and identified by mass spectrometry.

The determination of bismuth activity as an indicator of non-ionic surfactants also suffers from interference in environmental samples. Substance group specific methods also failed to detect different types of fluorine-containing anionic, cationic and non-ionic surfactants. Already marginal modifications in the precursor surfactant due to primary degradation or advanced metabolisation implicated their lack of detection [45]. 

Chemistry of sulfhydryl-specific modification. Reaction of MTS (CH3SO2SCH2CH2X) with a cysteine will lead to specific modification of the SH group by MTS. Note that X = NH+ (MTSEA), SO3- (MTSES), N(CH3)+ (MTSET), NH-biotin (MTSEA-biotin) or NHCO(CH2)5 (MTSEA-biotincap)... 

Bourel-Bonnet L, GrasMasse H, Melnyk O. A novel family of amphilic alpha-oxo aldehydes for the site-specific modification of peptides by two palmi-toyl groups in solution or in liposome suspensions. Tetrahedron Lett 2001 42 6851. 

Another a, i-unsaturated aldehyde analyzed is cinnamaldehyde. Its liquid-phase hydrogenation has been studied in our research group [20, 51, 94], using Pt, Ni and Cu-based tin-modified hi- and organobimetaUic catalysts (in all cases with Si02 as support). The catalytic results obtained showed that in aU cases there was a marked promoting effect of Sn on the selectivity to cinnamic alcohol (UOL). The specific modification of the monometallic systems due to Sn addition from the application of SOMC/M markedly increases the selectivity to UOL, especially in the case of Ni, where it goes from zero selectivity for the monometallic to 25% for the NiSn catalyst. Pt-based systems modified by Sn yield the best Suol values. 

From differences between the spectral (29) and fluorescence (SO) properties of the inhibited and uninhibited nuclease and from differences in the number of groups susceptible to acetylation (32) in the two forms of the enzyme, Cuatrecasas et al. (S3) concluded that tyrosyl residues were involved in binding pdTp. This led them to some very interesting studies of the specific modification of certain tyrosyl residues with tetranitromethane and of the properties of these modified forms of the nuclease which we will discuss below in the context of this paper. Briefly, the pattern of relative reactivity was found to be... 

Moore, M. J., and Sharp, P. A. (1992). Site-specific modification of pre-mRNA The 2,-hydroxyl groups at the splice sites. Science 256, 992—997. 

Group-specific chemical modification remains a useful method for studies of structure-function relationships in protein molecules, although unambiguous identification of essential amino acid residues and elucidation of their function are nowadays accomplished mainly by X-ray crystallography and site-directed mutagenesis. Chemical modifications... 

The principle advantage of the physical labeling method is the possibility of receiving direct information about the structure, mobility and local micropolarity of certain parts of a molecular object of any molecular mass. Developments in synthetic chemistry, biochemistry and site-directed mutagenesis have provided researchers with a wide assortment of labels and probes, and have paved the way for the specific modification of protein function groups, including enzyme active sites. 

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