Catalytic Aspects of Enzymatic Racemization

Adams, Elijah

doi:10.1002/9780470122891.ch3

Cited by 66 publications

(8 citation statements)

References 198 publications

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“…This assumes the presence of sugar nucleotide exchange reactions that would effectively interconvert UDP-[U- C]Man. Although this might explain the similar enzyme activities observed, such an epimerization activity has never been reported (Leloir, 1951;Adams, 1976;Dalessandro and Northcote, 1977). Indeed, a radioactive xylan polymer with no incorporation of Man residues was synthesized from UDP-[ 14 C]Xyl by microsome proteins from corn cobs (Bailey and Hassid, 1966), further negating the activities for an interconversion of UDP-Xyl and GDP-Man.…”

Section: Analysis Of the Ptcsla1-mediated In Vitro Reaction Productsmentioning

confidence: 86%

The Cellulose Synthase Gene Superfamily and Biochemical Functions of Xylem-Specific Cellulose Synthase-Like Genes inPopulus trichocarpa

et al. 2006

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Wood from forest trees modified for more cellulose or hemicelluloses could be a major feedstock for fuel ethanol. Xylan and glucomannan are the two major hemicelluloses in wood of angiosperms. However, little is known about the genes and gene products involved in the synthesis of these wood polysaccharides. Using Populus trichocarpa as a model angiosperm tree, we report here a systematic analysis in various tissues of the absolute transcript copy numbers of cellulose synthase superfamily genes, the cellulose synthase (CesA) and the hemicellulose-related cellulose synthase-like (Csl) genes. Candidate Csl genes were characterized for biochemical functions in Drosophila Schneider 2 (S2) cells. Of the 48 identified members, 37 were found expressed in various tissues. Seven CesA genes are xylem specific, suggesting gene networks for the synthesis of wood cellulose. Four Csl genes are xylem specific, three of which belong to the CslA subfamily. The more xylem-specific CslA subfamily is represented by three types of members: PtCslA1, PtCslA3, and PtCslA5. They share high sequence homology, but their recombinant proteins produced by the S2 cells exhibited distinct substrate specificity. PtCslA5 had no catalytic activity with the substrates for xylan or glucomannan. PtCslA1 and PtCslA3 encoded mannan synthases, but PtCslA1 further encoded a glucomannan synthase for the synthesis of (1→4)-β-d-glucomannan. The expression of PtCslA1 is most highly xylem specific, suggesting a key role for it in the synthesis of wood glucomannan. The results may help guide further studies to learn about the regulation of cellulose and hemicellulose synthesis in wood.

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Section: Analysis Of the Ptcsla1-mediated In Vitro Reaction Productsmentioning

confidence: 86%

The Cellulose Synthase Gene Superfamily and Biochemical Functions of Xylem-Specific Cellulose Synthase-Like Genes inPopulus trichocarpa

et al. 2006

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“…One defining catalytic property of PLP is the large stabilization of the resulting α-imino carbanions (quinonoids), which may be generated by deprotonation [16], decarboxylation [17] or retroaldol cleavage [5] reactions of α-amino acids (Figure 2). It is logical to attribute this large carbanion stabilization to the pyridinium ion electron sink [18].…”

Section: Electrophilic Catalysis By Acetonementioning

confidence: 99%

Pyridoxal 5′-phosphate: electrophilic catalyst extraordinaire

Richard

Amyes

Crugeiras

et al. 2009

Current Opinion in Chemical Biology

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Studies of nonenzymatic electrophilic catalysis of carbon deprotonation of glycine show that pyridoxal 5'-phosphate (PLP) strongly enhances the carbon acidity of α-amino acids, but that this is not the overriding mechanistic imperative for cofactor catalysis. Although the fully protonated PLP-glycine iminium ion adduct exhibits an extraordinary low α-imino carbon acidity (pKa = 6), the more weakly acidic zwitterionic iminium ion adduct (pKa = 17) is selected for use in enzymatic reactions. The similar α-imino carbon acidities of the iminium ion adducts of glycine with 5'-deoxypyridoxal and with phenylglyoxylate shows that the cofactor pyridine nitrogen plays a relatively minor role in carbanion stabilization. The 5'-phosphodianion group of PLP likely plays an important role in catalysis by providing up to 12 kcal/mol of binding energy that may be utilized for transition state stabilization.

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“…However, another class of racemases operates without any cofactor (in particular, the addition of the pyridoxal phosphate cofactor does not influence the conversion reaction ). Examples are the proline, aspartate and glutamate racemases from different bacteria . Isotope‐exchange studies indicated that all the pyridoxal phosphate‐independent racemases employed a ‘two‐base’ mechanism to catalyse epimerisation, and studies using chemical modifications and site‐directed mutagenesis revealed that these enzymes utilised their two cysteinyl residues as the proton abstractor and the proton donor .…”

Section: Isomerisation Of Peptides In Animalsmentioning

confidence: 99%

“…a polysaccharide cross‐linked with a short peptide), an essential constituent of the cell wall of Gram‐positive and Gram‐negative bacteria (Figure ) (review in ). The synthesis of the bacterial cell wall is believed to start with uridine diphosphate (UDP)‐ N ‐acetylmuramic acid, to which assorted free amino acids are added ( l ‐Ala, d ‐Glu and meso ‐diaminopimelic acid) to generate UDP‐ N ‐acetylmuramyl‐ l ‐Ala‐ d ‐Glu‐ meso ‐diaminopimelate ( cited in ). Then, a d ‐Ala dipeptide is coupled to this intermediate of synthesis by UDP‐ N ‐acetylmuramoyl‐tripeptide‐ d ‐Ala‐ d ‐Ala ligase.…”

Section: Incorporation Of Free D‐amino Acids Before or During Peptidementioning

confidence: 99%

Biogenesis of d‐amino acid containing peptides/proteins: where, when and how?

Ollivaux

Soyez

Toullec

2014

Journal of Peptide Science

110

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Peptides and proteins are chiral molecules with their structure determined by the composition and configuration of the amino acids constituting them. Natural amino acids (except glycine) display two chiral types (l- and d-enantiomers). For example, the presence of octopine, a derivative of l-arginine and d-alanine in octopus, or peptidyl poly-d-glutamic acid in a bacterial cell wall was demonstrated in the 1920s and 1930s, respectively. Nevertheless, an old dogma in biology was that proteins (in a strict sense) are composed of amino acids in the l-configuration exclusively, until a d-alanyl residue was reported in a frog skin opioid peptide in the early 1980s, and since, numerous d-amino acid containing peptides (DAACPs) have been discovered in multicellular organisms. Several hypotheses may be formulated to explain the origin of a d-residue in the peptide/protein chain. It may result from different mechanisms such as incorporation of a d-amino acid, non-enzymatic racemisation associated with ageing or diseases and enzymatic posttranslational modification. In the last case, the DAACPs are synthesised via a ribosome-dependent manner, and a normal codon for l-amino acid is present in the mRNA at the position where the d-residue is processed in the mature peptide by peptidyl aminoacyl l-d isomerisation, a peculiar and subtle posttranslational modification. In this review, the different pathways of biogenesis of DAACPs not only in bacteria but also in multicellular organisms are discussed, along with the description of the cellular specificity, the enzyme specificity and the substrate specificity of peptidyl aminoacyl l-d isomerisation.

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Catalytic Aspects of Enzymatic Racemization

Cited by 66 publications

References 198 publications

The Cellulose Synthase Gene Superfamily and Biochemical Functions of Xylem-Specific Cellulose Synthase-Like Genes inPopulus trichocarpa

The Cellulose Synthase Gene Superfamily and Biochemical Functions of Xylem-Specific Cellulose Synthase-Like Genes inPopulus trichocarpa

Pyridoxal 5′-phosphate: electrophilic catalyst extraordinaire

Biogenesis of d‐amino acid containing peptides/proteins: where, when and how?

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