Activation of amino acids

As an activator of the phosphokinases, magnesium is essential in energy-requiring biological processes, such as activation of amino acids, acetate, and succinate synthesis of proteins, fats, coen2ymes, and nucleic acids generation and transmission of nerve impulses and muscle contraction (67). 

Selective protection and activation of amino acids and peptides has now reached a highly sophisticated level and requires specialised knowledge for the most efficient use. 

The APFl gene product, a common factor of unknown function which increases the activity of amino acid permeases... 

Syntheses of Peptides via Carboxyl-Activation of Amino Acids... 

Another -activation of amino acids for peptide synthesis is achieved by preparing sulfenamides from sulfenylimidazoles. A sulfenylimidazole is formed in situ from the sulfenyl chloride (prepared from the disulfide and chlorine) and imidazole, which reacts further with an amino acid ester to give a sulfenamide in high yield. Conversion of such sulfenamides with IV-acyl amino acids by means of triphenylphosphine affords dipeptides with racemization of less than 0.5%.[481... 

A ribozyme activity that led to RNA-modifications that are analogous to the 5 -5 pyrophosphate caps of eukaryotic RNA transcripts was selected by Huang and Yarns [84]. Actually the author s intention was to isolate ribozymes which catalyze the formation of a mixed anhydride between an amino acid carboxylate and a 5 -terminal phosphate of an RNA, an activity that is chemically analogous to the activation of amino acids by ATP catalyzed by aminoacyl tRNA synthetases. However, while the selected ribozymes did... 

Figure 3.7 (a) Activation of amino acids by A-carboxyanhydride and (b) their condensation. (Adapted from Ferris, 2002.)... 

The activation of amino acids before their polymerization into proteins (see Fig. 27-14) is accomplished by an analogous set of reactions in which a transfer ENA molecule takes the place of coenzyme A An interesting use of the cleavage of ATP to AMP and PP, occurs in the firefly, which uses ATP as an energy source to produce light flashes (Box 13-2). 

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). 

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... 

Matsumoto, T. Yoshida, D. Mizusaki, S. Okamoto, H. Mutagenic activity of amino acid pyrolyzates in Salmonella typhimurium TA 96. Mutat. Res. 1977, 48, 279-86. 

Acidic proteinoid potentiates the active structure of lysine-rich proteinoid participating in forming microspheres in neutral buffer. Physical surface effects and providing micro condition in the microspheres could be surmised. Activation of amino acids generally requires acidic condition. Amino acids are activated by ATP and Mg2+ at pH 4-5 32 33). Aminoacyl adenylate anhydride and ester is formed preferentially from amino acid and adenylate imidazolide at pH 6.0J7). On the other hand, polycondensation of activated amino acids undergoes at pH values higher than 7. Peptides are formed from aminoacyl adenylate in basic buffer (the optimum pH is 10 for alanyl adenylate 40) from amino acid adenylate phosphoramidate and imidazole at pH 7.0 from N-(aminoacyl)-imidazole at pH 6-9 43). In this context, acidic and basic environments may be provided inside and/or on the surface of the microspheres composed of acidic and basic proteinoids in neutral buffer. Acidic micro condition suitable for the activation of amino acids and basic micro environment favorable for peptide formation from activated amino add may be provided. 

Table 4 Activation of Amino Acids and Related Compounds by ACV Synthetases as Determined by Amino Acid-Dependent ATP-[32P]PPi Exchange...

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... 

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). 

Huber C, Wachtershauser G. Peptides by activation of amino acids with CO on (Ni,Fc)S surfaces implications for the origin of life. Science 1998 281 670-2. 

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-... 

Be able to describe the mechanisms and requirements for activation of amino acids. 

ACTIVATION OF AMINO ACIDS AND FORMATION OF AMINOACYL-tRNAs... 

The molecular mechanism of translation in eukaryotes is very similar to that in bacteria. The activation of amino acids and attachment to tRNAs and the steps of initiation, elongation, and termination of polypeptide chains are essentially the same in overall terms. The small and large ribosomal subunits of bacteria and eukaryotes are equivalent with respect to their roles in initiation and elongation of chains. 

The synthesis of the pentapeptide moiety is supposed to start with a UDP-activated glutamic acid residue followed by the stepwise formation of UDP-activated peptides up to a pentapeptide. UDP was directly linked to the -amino group of the glutamic acid residue, a type of activation of amino acids previously not found in nature. Finally, the UDP-activated pentapeptide is linked to the disaccharide to give a UDP-activated disaccharide pentapeptide. 

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