Amino acids, syntheses determination

The sequence of each different peptide or protein is important for understanding the activity of peptides and proteins and for enabling their independent synthesis, since the natural ones may be difficult to obtain in small quantities. To obtain the sequence, the numbers of each type of amino acid are determined by breaking down the protein into its individual amino acids using concentrated acid (hydrolysis). For example, hydrolysis of the tetrapeptide shown in Figure 45.3 would give one unit of glycine, two units of alanine, and one unit of phenylalanine. Of course, information as to which amino acid was linked to which others is lost. 

The first example of a dynamic flux analysis was a study performed in the 1960s [269]. In the yeast Candida utilis, the authors determined metabolic fluxes via the amino acid synthesis network by applying a pulse with 15N-labeled ammonia and chasing the label with unlabeled ammonia. Differential equations were then used to calculate the isotope abundance of intermediates in these pathways, with unknown rate values fitted to experimental data. In this way, the authors could show that only glutamic acid and glutamine-amide receive their nitrogen atoms directly from ammonia, to then pass it on to the other amino acids. 

Note Presented here is a summary of data from one of the early experiments designed to elucidate the genetic code. A synthetic RNA containing only A and C residues in a 5 1 ratio directed polypeptide synthesis, and both the identity and the quantity of incorporated amino acids were determined, Based on the relative abundance of A and C residues in the synthetic RNA, and assigning the codon AAA (the most likely codon) a frequency of 100, there should be three different codons of composition A2C, each at a relative frequency of 20 three of composition AC2, each at a relative frequency of 4,0 and CCC at a relative frequency of 0.8. The CCC assignment was based on information derived from prior studies with poly(C), Where two tentative codon assignments are made, both are proposed to code for the same amino acid. 

Rate-determining step, hydroformylation, 163 Reactivity, enantiomers, 286 Recognition, enantiomers, 278 Reduction and oxidation, 5 Reductive coupling, dissolving metal, 288 Reductive elimination, 5, 111 Resolution. See Kinetic resolution Rhenium-carbene complexes, 288 Rhodium-catalyzed hydrogenation, 17, 352 amino acid synthesis, 18, 352 BINAP, 20... 

Enzymes are structurally complex, highly specific catalysts each enzyme usually catalyzes only one type of reaction. The enzyme surface binds the interacting molecules, or substrates, so that they are favorably disposed to react with one another (fig. 1.15). The specificity of enzyme catalysis also has a selective effect, so that only one of several potential reactions takes place. For example, a simple amino acid can be used in the synthesis of any of the four major classes of macromolecules or can simply be secreted as waste product (fig. 1.16). The fate of the amino acid is determined as much by the presence of specific enzymes as by its reactive functional groups. 

As the model suggests, the dietary need for amino acids is determined by the rates of depletion of the free amino acid pool by oxidation or synthesis of protein. During steady state conditions, the contribution to the free pool from dietary intake and protein breakdown should be exactly balanced by the flux out of the pool to synthesis and oxidation. Any condition that increases deposition of protein in the body or the rate of amino acid oxidation should produce an increased need for protein. For example, muscle hypertrophy is dependent on a positive balance of the protein turnover process. If synthesis of protein exceeds the catabolism of protein, then muscle mass will increase and the free amino acid pool would be depleted. Thus, a net increase in protein requires an increase in intake or a decrease in oxidation. Likewise, the same arguments hold for an increase in oxidation of amino acids. 

Tyrocidine B, C H N O,]. Purification and amino acid sequence determination King, Craig, J. Am. Chem. Soc. 77, 6624, 6627 (1955). Synthesis Kuromizu, Izumiya, Experi-entia 26, 587 (1970). Possesses the same structure as tyrocidine A except that L-tryptophan replaces the l phenylalanine. Crystals from methanol + isopropyl ether. 

Dauwe and Buddrus [12] tested a series of chiral amines for their ability to discriminate between the enantiomers of several acidic compounds. Strong basic amidines, as shown in Figure 6-8, turned out to be suitable for the resolution of even weak acidic compounds such as phenols, barbiturates and alcohols. The same group [13] developed chiral palladium complexes with diamines for discrimination of a-amino acids and determination of enantiomeric excess resulting from asymmetric synthesis. 

In protein synthesis, the selection of a particular amino acid is determined by the so-called genetic code, or a sequence of three bases in DNA. Will a sequence of only two bases unambiguously determine the selection of 20 amino acids found in proteins Explain. 

The observations on the histidine operons described above clearly show that all the enzymes with amino acid sequences determined by the histidine operon are not synthesized in equimolecular amounts. But the rate at which each of the proteins is synthesized is determined by the position of the cistron within the operon. The amount of protein synthesized decreases the further the cistron is from the operator gene. Furthermore, mutations that interfere with the biosynthesis of one enzyme of the histidine pathway lead to a reduction of the rate of synthesis of all the enzymes with structures dictated by cistrons distal to the mutated cistron. 

We investigated the biosynthesis of component amino acids of glutathione (GSH) in vitamin-Bi2 or folic-acid deficient rats (1). Glycine-2-C or L-cystine-S was administered intraperitoneally to normal or the deficient rats. Liver GSH was determined, then isolated, and the radioactivity of GSH and its component amino acids was determined. The extent of incorporation of either glycine-2-C or cysteine-S into the respective moieties of GSH was not appreciably affected by either deficiency, indicating that neither vitamin is involved in the sjrstems which catalyze the synthesis of GSH from glycine, cysteine, and glutamic acid, a conclusion which is in accord with those of Bloch (2) and Snoke and Rothman... 

Translation The stepwise synthesis of a polypeptide with an amino acid sequence determined by the nucleotide sequence of the mRNA coding region. The genetic code relates each amino acid to a group of three... 

Once synthesis has been initiated, the protein is elongated through a series of successive additions of amino acids as determined by the messenger RNA template. Each new amino acid is linked to the next by the formation of a peptide b)ond. Eventually the procedure will be terminated... 

Acyl carrier protein (ACP) plays a central rOle In lipid metabolism, serving as both a component of plant fatty acid synthetase (1) and as a substrate/cofactor for complex lipid biosynthesis (2). The protein has been purified from a number of plant sources and Its amino acid sequence determined for the protein from both barley leaf (3) and spinach leaf (4) material. Both of these two previously mentioned sources of ACP have two detectable forms of the protein (5-6) whilst in seed material only one form has been detected (5). ACP has been shown, using immunological techniques, to be a developmentslly regulated protein In maturing soy bean seeds. The activity of the protein appearing just prior to lipid accumulation (7). Despite the Importance of this protein in lipid metabolism and the fact that seeds are a major site of lipid synthesis there Is no reported literature on the characterization of ACP from seed material. The present study was aimed at a detailed characterization of ACP from rape (Brassica napus ) seed ... 

Jaksic, T, F. Jahoor, P.J. Reeds and W.C. Heird, 1994. The determination of amino acid synthesis in human neonates using a glucose stable isotope. Sutg. Forum 44, 642-686. 

Two groups recently achieved in silico identification for ACL racemases by identifying Lys241 as a key amino acid residue [27, 28]. ACL and amino acid amide-racemizing activities were detected among tens of candidates [27]. These newly discovered ACL racemases may be useful for chiral amino acid synthesis by dynamic kinetic resolution and for determining the xmknown physiological functions of ACL racemases. 

Many amino acids have specific functions or support specific functions by serving as precursors or substrates for reactions in which vital end products are produced. The availability of amino acids to serve these purposes is determined by the rate at which they are released into the plasma and other pools in which these reactions take place, as well as by the rate of disappearance through excretion, protein synthesis, or conversion to other amino acids. The rate of this release, referred to as amino acid flux, is determined by the breakdown of (dietary) proteins or the conversion from other amino acids. Increased demand for one or more amino acids generally leads to an increased flux of the required amino acids across specific organs. Since it is the flux of an amino acid that determines its availability for metabolic processes, the flux is far more important for maintenance of specific functions than the plasma concentration. In fact it is striking that fluxes of... 

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