Proteins directed modification, Table

Due to its high reactivity, NO can interact and react with many effector proteins. Targets are proteins with boimd metal ions and specific cysteine residues of proteins. In Table 6.3, some important bioregulatory proteins are summarized, for which direct modification by NO is assumed. Two target proteins should be mentioned in particular ... 

Several amino acyl constituents crucial for the protein s function are particularly vulnerable to radical damage (Roshchupkin et al., 1979 Singh et al., 1982 Sies, 1986), as shown in Scheme 2.2 and Table 2.2, with the consequences of oxidative modification. It is generally accepted that reactive oxygen species can react directly at several of these sites on a protein in addition, in some instances, when protein radicals are formed at a specific amino acyl site, they can be rapidly transferred to other sites within the protein infrastructure, the pathway so far proven being illustrated in Fig. 2.14 (Butler et al., 1988). 

Table 15.5 shows examples of nominal, monoisotopic, and average mass values. Although the differences between nominal and average values may appear small, especially for elemental species, they become larger as molecular complexity increases and are important in establishing the identities of proteins. In particular, site-directed mutagenesis and posttranslational modification studies require accurate average mass values to confirm the identities of product proteins. 

Table III lists the most commonly encountered amino acid derivatives formed by in vivo modification of proteins during or after the completion of their ribosome-directed biosynthesis. In contrast to the strict alphabetical listing of Table II, the entries of this table have been organized in groups relative to the parent amino acid. It should be noted that this list is not exhaustive. There are several reports of covalent prosthetic group attachment to proteins through the side chains of a variety of residues (see Glazer et a/., 1975). In addition, carbohydrate is often found attached to proteins (Kornfeld and Kornfeld, 1976 Waechter and Lennarz, 1976) and there are reports of covalently bound lipid as well (Braun and Bosch, 1972 Stoffyn and Folch-Pi, 1971). However, for the most part, these amino acids have not been isolated as defined entities. A brief description of amino acid derivatives formed in vivo and their origin is given below.

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