Activation of amino acids, for protein

Another way in which the phosphorylation state of the adenylate system can regulate the cycle depends upon the need for GDP in step/of the cycle (Fig. 17-4). Within mitochondria, GTP is used largely to reconvert AMP to ADP. Consequently, formation of GDP is promoted by AMP, a compound that arises in mitochondria from the utilization of ATP for activation of fatty acids (Eq. 13-44) and activation of amino acids for protein synthesis (Eq. 17-36). 

The material within the cell membrane is gellike and is termed the cytoplasm or cytosol. It is composed of ions, water, soluble proteins, and enzymes that are involved in generation of energy in the form of ATP by a process termed the tricarboxylic acid cycle (TCA) or Krebs cycle in the absence of oxygen (Figure 1.4). It is also involved in activation of amino acids for protein synthesis (Table 1.5 and Figure 1.4). 

How many high-energy phosphate-bond equivalents are utilized in the process of activation of amino acids for protein synthesis ... 

In the activation of amino acids for protein biosynthesis, the aminoacyl-tRNA synthetases catalyze their ligation as acyl esters to the 3-hydroxyl ends of their cognate species of tRNA. The chemical activation mechanism requires ATP and occurs in two steps, the activation of the amino acid by reaction with ATP to form an aminoacyl adenylate in reaction (29a), and the transfer of the activated aminoacyl group to the 3 -hydroxyl end of tRNA in reaction (29b) (88). 

RCOOH + ATP RCO-AMP (enzyme-bound) PPi as does the activation of amino acids for protein S3mthesis. 

Mechanism of Activation of Amino Acids for Protein Synthesis. 220... 

Activation of amino acids for incorporation into oligopeptides and proteins can occur via two routes of acyl activation. In the first of these an acyl phosphate (or acyl adenylate) is formed and reacts with an amino group to form a peptide linkage (Eq. 13-4). The tripeptide glutathione is formed in two steps of this type (Box 11-B). In the second method of activation aminoacyl... 

Peptidases and proteases play essential 48 roles in protein activation, cell regulation and signaling, in the generation of amino acids for protein synthesis or utilization in other metabolic pathways. 

M. . Krahl Dr. Anfinsen mentioned an attempt to test the possibility that GSH may serve as a source of amino acid for protein synthesis. There may be a n unber of other people who have done negative experiments of this sort. I am one of them. With S Mabeled cysteine and S -labeled GSH, which were kindly supplied by Dr. Tabern and Dr. Hostattler, I measured the amount of S activity incorporated into a crude protein fraction by liver slices in vitro. The molar concentration of cysteine and GSH in the incubation medium was the same in the two respective experiments and the protein fraction was one which had been put through performic-acid treatment. We presume that whatever S was there was not merely attached to the protein via —S—S— linkages. The S was incorporated into this protein fraction 10 times as rapidly from cysteine as it was from GSH. This may mean quite a few things, but gives no support, unfortunately, to the idea that GSH may be an intermediate between cysteine as an amino acid and cysteine in peptide linkage in protein. 

First attempts to use the carbonate or the carbamate function for the covalent binding of amino acids and proteins applying the activation of dextran with phosgene showed that this approach is limited due to the fact that it is combined with a number of side reactions (Fig. 51) [355]. 

The synthesis of unnatural amino acids and peptides is of great interest since it offers the possibility to design new biologically active protein analogues. One of the possible interesting transformations is side chain oxidation of amino acids, for which MTO can be used. It is reported that various /V-Boc protected amino acids such as methionine (Met), cysteine (Cys), and tryptophan (Trp) can be oxidized with the MT0/H202 system [108]. 

In this scenario, the next key step was the discovery by early living organisms of alternative pathways to synthesize nucleoside triphosphates (stage 3 in Scheme 40), for instance by the introduction of an oxido-reduction metabolism. In the particular case of ATP, the increase in its concentration could have forced the chemical flux of the system to be reverted since the unstable adenylate anhydride was stabilized in the active site of the adenylate binding protein (E) allowing the activation of amino acids by ATP through the process that became predominant. 

Cytosol or cytoplasm Water, ions, soluble proteins Contains enzymes and structures for generation of energy (ATPa) in the absence of oxygen (TCAb cycle), activation of amino acids, carrying out specialized cell functions... 

Enzyme-catalyzed attachment of amino acids to proteins represents an attractive and interesting way for improving the nutritional value of food proteins. The enzymes that participate in the gastrointestinal digestion of food proteins catalyze exclusively hydrolytic reactions under physiological conditions. However the synthetic activity of proteolytic enzymes was reported first by Danilewski in 1886, and more recently a number of studies have been devoted to plastein formation from con-... 

Figure 2. General scheme for covalent attachment of amino acids to proteins by the active-esters method. Reaction conditions are described in Ref. 22 TFA = trifluoroacetic acid.

Jhe synthesis of proteins, as characterized by the in vitro incorporation of amino acids into the protein component of cytoplasmic ribonu-cleoprotein, is known to require the nonparticulate portion of the cytoplasm, ATP (adenosine triphosphate) and GTP (guanosine triphosphate) (15, 23). The initial reactions involve the carboxyl activation of amino acids in the presence of amino acid-activating enzymes (aminoacyl sRNA synthetases) and ATP, to form enzyme-bound aminoacyl adenylates and the enzymatic transfer of the aminoacyl moiety from aminoacyl adenylates to soluble ribonucleic acid (sRNA) which results in the formation of specific RNA-amino acid complexes—see, for example, reviews by Hoagland (12) and Berg (1). The subsequent steps in pro-... 

Transfer RNA (tRNA) has the lowest molecular weight, that is, near 28,000. Its function is to activate amino acids for protein biosynthesis. It has a unique cloverleaf structure (Figure 10.29), and there are sections of double-helix, bulges, and hairpin turns. Of all RNAs, it has the highest number of unusual bases (10-15%). Thus, the hairpin arm pointing east contains pseudouridine W and is... 

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