Although B. subtilis synthesizes proline from glutamate , , , S. aureus preferentially utilizes arginine rather than glutamate as a precursor for proline biosynthesis via arginase (RocF), ornithine aminotransferase (RocD), and P5C reductase (ProC) . Furthermore, Li and colleagues recently reported that proline biosynthesis is regulated through CcpA-mediated carbon catabolite repression at both rocF and rocD. Carbon catabolite repression allows bacteria to preferentially utilize preferred carbon sources and therefore increase the organism's fitness . The trans-acting carbon catabolite protein CcpA in a complex with Hpr binds to cis-acting DNA sequences known as catabolite responsive elements (CRE) , , , . In the presence of a preferred carbon source, HprK phosphorylates the Ser-46 position of Hpr and once phosphorylated, Hpr binds to CcpA , , .
Nine of 12 nonessential amino acids are synthesised from amphibolic intermediates, whereas three amino acids (tyrosine, cysteine and hydroxylysine) derive from essential amino acids. Amino acid transaminases, glutamate dehydrogenase and glutamine synthetase play a central role in the synthesis of nonessential amino acids.
Of these, 61 code for amino acids.
The mRNA strand bearing the transcribed code for synthesis of a proteininteracts with relatively small RNA molecules (about 70-nucleotides) to whichindividual amino acids have been attached by an ester bond at the 3'-end.
Biosynthesis and metabolism of arginine in bacteria.
Three major feedback mechanisms cooperate in regulating the overall rate ofde novo purine nucleotide synthesis and the relative rates of formation of thetwo end products, adenylate and guanylate (Fig. 16–3). The first mechanism isexerted on the first reaction that is unique to purine synthesis—transfer of anamino group to PRPP to form 5-phosphoribosylamine. This reaction is catalyzed bythe allosteric enzyme glutamine-PRPP amidotransferase, which is inhibited by theend products IMP, AMP, and GMP. AMP and GMP act synergistically in thisconcerted inhibition. Thus, whenever either AMP or GMP accumulates to excess,the first step in its biosynthesis from PRPP is partially inhibited.
In the second control mechanism, exerted at a later stage, an excess of GMP inthe cell inhibits formation of xanthylate from inosinate by IMP dehydrogenase,without affecting the formation of AMP (Fig. 16–3). Conversely, an accumulationof adenylate inhibits formation of adenylosuccinate by adenylosuccinatesynthetase, without affecting the biosynthesis of GMP. In the third mechanism,GTP is required in the conversion of IMP to AMP (Fig. 16–2, step 1), whereas ATPis required for conversion of IMP to GMP (step 4), a reciprocal arrangement thattends to balance the synthesis of the two ribonucleotides.
The final control mechanism is the inhibition of PRPP synthesis by theallosteric regulation of ribose phosphate pyrophosphokinase. This enzyme isinhibited by ADP and GDP, in addition to metabolites from other pathways ofwhich PRPP is a starting point.
The Handbook of Microbial Metabolism of Amino Acids
Stühlinger MC, Tsao PS, Her JH et al. (2002) Homocysteine impairs the nitric oxide synthase pathway: role of asymmetric dimethylarginine. Circulation 104(21): 2569–2575.
and metabolism of arginine in bacteria
(C00072), which is a necessary coenzyme in tyrosine metabolism, or (C00250), which is required for tryptophan metabolism, cause deficiencies in the metabolism of aromatic amino acids.