Amino acids Serine Ser

A certain polypeptide is shown by arid hydrolysis to contain only three amino acids serine(Ser), alanine(Ala), and methionine(Met) with mole fractions of j, and respectively. Enzymatic hydrolysis yields the following fragments Ser-Ala Ser-Met Ala-Ser. Deduce the primary structure of the polypeptide. 

In order to verify this assumption, we studied the temperature dependence of the kinetic isotope effect during hydrolysis of some specific substrates, i.e. amino acid esters, by serine proteases like a-chymotrypsin[468,469] and 3-trypsin[470]. It is well known that a two-stage hydrolysis mechanism takes place for this class of enzymes with the formation, as an intermediate product, of an acyl derivative of the amino acid serine (Ser-195), a constituent of the polypeptide chain of the protein. The side group (-CH2OH) of serine is located in the region of the active center[471-474] ... 

In both cases, histidine fragment is activated by the corresponding amino-acid fragment (Ser (serine) 113 for catalase and Asn 82 for peroxidase). 

Protein kinases like glycogen-phosphorylase kinase act on specific amino-acid sequences, called consensus sequences. Protein-kinase-a acts on the serine/threonine residue in the sequence X-arg-arg/lys-X-ser/thr-asx. Cyclin-dependent-kinase-2 acts on the same residues in the sequence X-ser/thr-pro-X-lys/arg. Only the alcoholic amino acids serine, threonine and tyrosine can be phosphorylated. 

In RmL the nucleophilic triad consists of Ser-144, Asp-203, and His-257, whereas in hPL the analogous amino acids are Ser-153, Asp-177, and His-264. All hydrogen bonds identified in this system are analogous to those observed in serine proteinases Ne2 of the histidine is bonded to the serine hydroxyl, and N31 is H-bonded to the aspartic acid (Fig. 4). Further details of the H-bonding stereochemistry are given in Table II. 

Sheehan and co-woricers prepared a pentapeptide, L-Thr-L-Ala-L-Ser-L-His-L-Asp as an esterase model, from a viewpoint that three amino acids (serine, histidine and aspartic acid) are involved at the active site 131,132). The rate constant for the pentapeptide if, 1.5 sec (pH 7.73,25.5°) is greater than 0.25 M sec for tripeptide L-Gly-L-His-L-Ser and 0.3 M sec for imidazole. Not much rate enhancement was observed also for the cyclic dimer of the tripeptide. Subsequently, they conducted the solvolysis of an amino acid derivative 70 by oligopeptides, 11 and L-Ser-7-aminobutyl-L-His-7-aminobutyl-L-Asp72. 

Mechanisms of Serine Hydrolases. Typical to enzymatic reactions, the enzyme (E) first binds its substrate (S) at the active site as an enzyme-substrate complex (E S). For the formation of the product P, the enzyme-catalyzed reaction then takes place through the mechanism typical of the enzyme. At the active site of serine hydrolases (lipases, carboxylesterases, and serine proteases), the catalytic machinery is called a cataljdic triad consisting of amino acid residues Ser, His, and either Asp or Glu (Fig. 5). In the E S complex, imidazole of His serves as a general acid/base catalyst, catalyzing the addition of the alcoholic hydroxyl of the serine residue to the carbonyl carbon of the acyl donor (R C02R, the first substrate S ). This leads both to the liberation of the first product P (R OH) and to the formation of the so-called acyl-enzyme intermediate. This ester intermediate then reacts with the second substrate (R OH), which leads to the... 

Two reastant populations in Kyoto (KTMr and KTNr) showed a high level of genetic similarity, and had the same alteration from proline (Pro) to alanine (Ala). In Yamagata, 2 resistant populations (YCGr and YSSr) were genetically similar, but had different amino acid substitutions (Ser and Gin). One of the resistant populations in Yam ata (YCGr) had the same alteration fiom Proline (Pro) to serine (Ser) as a resistant population in Akita (AKTr), but tiiey showed a relatively low level of gen ic similarity. Two resistant populations in Akita (AKTr and ASTr) were not genetically similar, and had different amino acid substitutions (Ser and Lys). 

Glutamic acid production. 30-35 g/1 Glu raw solution contains additional amino acids Ala, Ser, and Thr (5-7 g/1 of each). The treatment is performed in one or two stages. An additional step can be performed to obtain serine as a secondary product. 

It is a peptide containing 27 amino acid residues containing the amino acids L-histidine (His) L-aspartic acid (Asp) L-serine (Ser) glycine (Gly) L-threonine (Thr) L-phenyl-alanine (Phe) L-glutamic acid (Glu) L-glutamine [Glu(NHj)] L-leucine (Leu) L-arginine (Arg) L-alanine (Ala) and L-valinamide (Va -NHj). 

Strategy Write the condensation reaction that takes place between glycine and serine. To do this, start with the structural formulas of the two amino acids, glycine at the left, serine at the right. In each case, put the NH2 group at the left, the COOH group at the right. Condense out a water molecule what is left is the structural formula of Gly-Ser. 

In addition, eNOS is subject to protein phosphorylation. It can be phosphotylated on several serine (Ser), threonine (Thr), and tyrosine (Tyr) residues however, major changes in enzyme function have been reported for the phosphorylation of amino acid residues Seri 177 and Thr495 (in the human eNOS sequence) (Fig. 3). 

The family of serine proteases has been subjected to intensive studies of site-directed mutagenesis. These experiments provide unique information about the contributions of individual amino acids to kcat and KM. Some of the clearest conclusions have emerged from studies in subtilisin (Ref. 9), where the oxyanion intermediate is stabilized by t>e main-chain hydrogen bond of Ser 221 and an hydrogen bond from Asn 155 (Ref. 2). Replacement of Asn 155 (e.g., the Asn 155— Ala 155 described in Fig. 7.9) allows for a quantitative assessment of the effect of the protein dipoles on Ag. ... 

Amino acid abbreviations aa, generic amino acid Ala, L-alanine Aib, 2-aminoisobutyric acid Cys, L-cysteine Asp, L-aspartic acid Glu, L-glutamic acid Gly, glycine Lys, L-ly-sine Ser, L-serine Trp, L-tryptophan Ser, 2-amino-3-(5-methyl-2,4-dioxo-3,4-dihydro-2H-... 

The R2C2 complex has no enTymatic activity, but the binding of cAMP by R dissociates R from C, thereby activating the latter (Figure 43-5). The active C subunit catalyzes the transfet of the y phosphate of ATP to a serine or threonine residue in a variety of proteins. The consensus phosphotylation sites are -Arg-Arg/Lys-X-Ser/Thr- and -Arg-Lys-X-X-Ser-, where X can be any amino acid. 

Other fibrous proteins contain extensive regions of pleated sheets. The fibers spun by a silkworm, for example, are made almost entirely of fibroin, a protein composed primarily of just three amino acids glycine (45%), alanine (30%), and serine (12%). Each chain of fibroin contains extensive regions where a sequence of six amino acids occurs repeatedly . .. -Gly-Ser-Gly-Ala-Gly-Ala-. .. Notice that every other amino acid is glycine, which is the smallest amino acid. This alternating arrangement is an important feature in the packing of the strands that make up the pleated sheet. 

NS3 is a 631 amino acid protein, and its first 180 amino acids encode a serine protease of the chymotrypsin family (Figure 2.2A). It has a typical chymotrypsin-family fold consisting of two jS-barrels, with catalytic triad residues at the interface. His-57 and Asp-81 are contributed by the N-terminal jS-barrel and Ser-139 from the C-terminal jS-barrel. NS3 and closely related viral proteases are significantly smaller than other members of the chymotrypsin family, and many of the loops normally found between adjacent jS-strands in trypsin proteases are truncated in NS3 [31]. Probably... 

---