Biological Oxidations and Reductions

Lipmann, Fritz

doi:10.1146/annurev.bi.12.070143.000245

Cited by 16 publications

(8 citation statements)

References 20 publications

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“…The mechanisms for polysaccharide biosynthesis are fundamentally different depending on whether the chain grows from the reducing or the nonreducing end (19,24). Robbins et al (19) first described these differences for hyaluronic acid in 1967.…”

Section: Discussionmentioning

confidence: 99%

“…The situation, however, is very different for chain elongation at the reducing end, because the seHAS cleaves this disaccharide-UDP linkage when the third sugar is added as in the reaction labeled (ii) in Scheme 2. During chain elongation at the reducing end the UDP-sugars are not the donors, but rather they are the acceptors (3,19,24). The donors are the hyaluronyl chains, which contain either GlcNAc or GlcUA at the reducing end and are activated by their attachment to UDP.…”

Section: Discussionmentioning

confidence: 99%

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Hyaluronan Biosynthesis by Class I Streptococcal Hyaluronan Synthases Occurs at the Reducing End

Tlapak-Simmons¹,

Baron²,

Gotschall

et al. 2005

Journal of Biological Chemistry

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Previous studies reached different conclusions about whether class I hyaluronan synthases (HASs) elongate hyaluronic acid (HA) by addition to the reducing or the nonreducing end. Here we used two strategies to determine the direction of HA synthesis by purified class I HASs from Streptococcus equisimilis and Streptococcus pyogenes. In the first strategy we used each of the two UDP-sugar substrates separately to pulse label either the beginning or the end of HA chains. We then quantified the relative rates of radioactive HA degradation by treatment with ␤-glycosidases that act at the nonreducing end. The results with both purified HASs demonstrated that HA elongation occurred at the reducing end. In the second strategy, we used purified S. Since the first HAS 1 was identified and cloned in 1993 (1, 2) we have learned much about the structure and function of these unusual glycosyltransferases (3-7). The molecular masses of the streptococcal (ϳ49 kDa) or eukaryotic (ϳ65 kDa) HASs are relatively small in view of the multiple functions mediated by these enzymes in order to synthesize HA (8). HAS binds UDP-glucuronic acid (UDP-GlcUA) and UDP-N-acetylglucosamine (UDP-GlcNAc) in the presence of MgCl 2 and catalyzes two distinct intracellular glycosyltransferase reactions. HAS also binds and translocates the growing HA chain through the enzyme, thereby extruding the polymer through the cell membrane, and releases the HA chain extracellularly after up to 50,000 monosaccharides (ϳ10 7 Da) have been assembled. Based on differences in protein structure and mechanism of action, the known HASs have been categorized into two classes (5). Class I members include HASs from Streptococcus, mammals, and other eukaryotes, whereas the bacterial HAS from Pasteurella multocida is the only class II member.Despite great progress in our understanding of HAS structure and function, there is still controversy regarding the direction of HA synthesis. Stoolmiller and Dorfman (9) concluded in 1969 that the streptococcal HAS adds new sugars to the nonreducing end of HA. In conflict with this result, Prehm in 1983 (10) and Asplund et al. in 1998 (11) performed studies with membranes from eukaryotic cells and concluded that HA synthesis occurs at the reducing end. Although differences in the contributions of the three mammalian HAS isoenzymes to these latter results were not considered, it is highly likely that the mechanisms of HA chain elongation for all of the class I HAS members are the same (3). Recently, Hoshi et al. (12) reported that recombinant truncated variants of human HAS2 expressed in Escherichia coli were able to synthesize short HA oligosaccharides by addition to the nonreducing end. Because the crude membranes used in all the above studies contain multiple glycosyltransferases, some of these reported results might have alternate interpretations. To resolve these conflicting results about the direction of HA synthesis, which is a fundamental mechanistic feature of HAS function, we performed several types of experiments using two...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Hyaluronan Biosynthesis by Class I Streptococcal Hyaluronan Synthases Occurs at the Reducing End

Tlapak-Simmons¹,

Baron²,

Gotschall

et al. 2005

Journal of Biological Chemistry

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“…Klein's reactivation (99) of dialyzed nucleosidase with phosphate or arsenate is recalled, and the mechanism of this reactivation now explained by identifying nucleosidase as a nucleoside phosphorylase. A role of ribose-1-phosphate in nucleotide synthesis had been suggested in an earlier review of this series (116) .…”

Section: Glucose-l-phosphate+enzymepglucose-enzyme+phosphatementioning

confidence: 89%

Intermediary Metabolism of Phosphorus Compounds

Lipmann¹,

Kaplan²

1949

Annu. Rev. Biochem.

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Although it had become rather clear that energy delivery from fermentative, as well as from oxidative, metabolism is geared through the generation of energy-rich phosphate bonds, there had existed until recently a vacuum on the receiving side. For a long time only relatively few instances of phosphate bond utilization were recognizable. During the last few years, however, the number of synthetic reactions driven by an influx of energy-rich phosphate bonds has increased impressively. Peptide formation (19,43,58,170), the synthesis of urea (40, 158), transmethylation from methionine (25), the synthesis of C\(-and {3-keto acids (93, 169.), of fatty acids (11), and the process of bioluminescence (131), to name the most important advances, appear now to belong into this group.In most cases as yet a general dependence of such condensations on the availability of adenosinetriphosphate (ATP) was recognized and little information has been gained about the nature of phos phorylated intermediaries expected to be formed. A promising, although still preliminary, advance has been made, however, to wards a final characterization of the phosphorylated acetyl precur sor (93), the intermediary in acetylation, in keto and fatty acid and, most likely, in citric acid synthesis (91). CONDENSATIONS INVOLVING ACETATE ACTIVATIONAcetoacetate splitting and synthesis.-After the discovery of the phosphoroclastic splitting of pyruvate (101, 187), an analogous reaction with acetoacetate appeared likely. Such phosphoroclastic splitting of acetoacetate to acetylphosphate and acetate has now been demonstrated with cell-free preparations of Clostridium kluyverii by Stadtman & Barker (174). A disappearance of inor-1

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“…By the end of 90 min, most of the moisture in the dhool would be lost due to aeration, leading to a drought effect in the dhool. In normal tea fermentation process, drought effect has also been reported to reduce the activity of polyphenol oxidase in the dhool [19].…”

Section: Effect Of Cfe Volume (Enzyme Activity)mentioning

confidence: 99%

Effect of Physicochemical Parameters on Enzymatic Biodecaffeination During Tea Fermentation

Babu¹,

Thakur

Patra³

2011

Appl Biochem Biotechnol

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We report for the first time the development of a biodecaffeination process for tea synchronised with tea fermentation process using enzymes isolated from Pseudomonas alcaligenes. Cell-free extract was used for biodecaffeination of tea during fermentation of tea and 80% of the caffeine in the tea dhool was degraded within 90 min of incubation. Several factors that tend to effect the biodecaffeination during this stage, like moisture, aeration, intermittent enzyme addition and mixing, were optimized, and inhibitory interactions of proteins with polyphenols, caffeine-polyphenol interactions, which directly influence the biodecaffeination process were prevented by the use of glycine (5% w/w) in the dhool. Tea decaffeinated through the enzymatic route retained the original flavor and aroma, and there was an increase in the total polyphenol content of the tea.

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Biological Oxidations and Reductions

Cited by 16 publications

References 20 publications

Hyaluronan Biosynthesis by Class I Streptococcal Hyaluronan Synthases Occurs at the Reducing End

Hyaluronan Biosynthesis by Class I Streptococcal Hyaluronan Synthases Occurs at the Reducing End

Intermediary Metabolism of Phosphorus Compounds

Effect of Physicochemical Parameters on Enzymatic Biodecaffeination During Tea Fermentation

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