Seryl alanine

N-[N-(benzyloxycarbonyI)-L-prolyl-L-aspart-4-oyl]-N-[N-(benzyloxycarbonyl)-L-seryl-L-aspart-l-oyl-(L-alanine methyl ester)-4-oyl]-... 

The amino acid components of peptides and proteins are linked together by amide bonds (see p. 60) between a-carboxyl and a-amino groups. This type of bonding is therefore also known as peptide bonding. In the dipeptide shown here, the serine residue has a free ammonium group, while the carboxylate group in alanine is free. Since the amino acid with the free NHs group is named first, the peptide is known as seryl alanine, or in abbreviated form Ser-Ala or SA. 

This enzyme [EC 3.4.16.4], also known as serine-type D-alanyl-D-alanine carboxypeptidase, catalyzes the hydrolysis of D-alanyl-D-alanine to yield two D-alanine. This enzyme comprises a group of membrane-bound, bacterial enzymes of the peptidase family Sll. They are distinct from the zinc D-alanyl-D-alanine carboxypeptidase [EC 3.4.17.14]. The enzyme also hydrolyzes the D-alanyl-D-alanine peptide bond in the polypeptide of the cell wall. In addition, the enzyme will also catalyze the transpeptidation of peptidyl-alanyl moieties that are A-acetyl-substituents of D-alanine. The protein is inhibited by j8-lactam antibiotics, which acylate the active-site seryl residue. 

Neither L-alanine nor L-cysteine was incorporated into (113), but both L-serine (112) and glycine were. Good evidence was obtained that utilization of glycine is by way of L-serine. L-Serine was utilized without loss of the tritium that was sited at C-3, so the construction of the /Mactam ring occurs without change in the oxidation state at this carbon atom,97 in contrast to the parallel situation in the biosynthesis of penicillins.2 For nocardicin A (113), direct nucleophilic displacement of a (presumably activated) hydroxy-group of a seryl unit by amide nitrogen apparently occurs. 

Amino acid analyses were performed on the glycopeptide preparation following hydrolysis of the polymer(s) in 6 N HCl for 22 hr. Approximately 38% of the amino acids were represented by seryl and threonyl residues (Table VI). In addition, the amino acid composition is similar to that obtained for both the extracellular and soluble "cytoplasmic" peptidophosphogalactomannans. The polypeptides contained only trace quantities of aromatic amino acyl residues, no detectable quantities of sulfur-containing amino acyl residues, and were rich in serine, threonine and alanine. 

An interesting approach to obtain peptides in which the purine or pyrimidine residues were correctiy spaced for interaction with the nucleic acids, was made by using a spacer amino acid [49]. Serine was used as a spacer and several protected tetrapeptides, e.g., a-N-t-BOC-L-seryl-D,L-P-(thymin-l-yl)ala-nyl-L-seryl-D,L-P-(thymin-l-yl)alanine, ethyl ester, were synthesized but little was reported about their solution properties and interactions with the nucleic acids. The polymerization of the nucleic acid base-substituted L-lysine derivatives by N-carboxyamino acid anhydride method was also reported [52, 53]. 

Each of the hydroxyproline-rich wall protein tryptides contains a pentapeptide of serine-(hydroxyproline)4, while most of the tryptides contain one or more galactosyl residues (85). One tryptide, which was found to contain 2 residues each of galactose and serine, was subjected to P-elimination by several different methods. The elimination procedures converted serine to alanine or cysteic acid with a concomitant release of free galactose (85). These results demonstrated the covalent attachment of a single galactosyl residue to each seryl residue in the... 

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