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Torreno VPM, Molino RJEJ, Junio HA, Yu ET. Comprehensive metabolomics of Philippine Stichopus cf. horrens reveals diverse classes of valuable small molecules for biomedical applications. PLoS One 2023; 18:e0294535. [PMID: 38055702 PMCID: PMC10699614 DOI: 10.1371/journal.pone.0294535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 11/02/2023] [Indexed: 12/08/2023] Open
Abstract
Stichopus cf. horrens is an economically important sea cucumber species in Southeast Asia due to their presumed nutritional and medicinal benefits. However, compared to other sea cucumbers such as Apostichopus japonicus, there are no biochemical studies on which compounds contribute to the purported bioactivities of S. cf. horrens. To address this, a high-throughput characterization of the global metabolite profile of the species was performed through LC-MS/MS experiments and utilizing open-access platforms such as GNPS, XCMS, and metaboAnalyst. Bioinformatics-based molecular networking and chemometrics revealed the abundance of phospholipids such as phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), phosphatidylinositols (PIs), and phosphatidylserines (PSs) in the crude samples. Body wall extracts were observed to have higher levels of structural, diacylated PCs, while the viscera have higher relative abundance of single-tail PCs and PEs that could be involved in digestion via nutrient absorption and transport for sea cucumbers. PEs and sphingolipids could also be implicated in the ecological response and morphological transformations of S. cf. horrens in the presence of predatory and other environmental stress. Interestingly, terpenoid glycosides and saponins with reported anti-cancer benefits were significantly localized in the body wall. The sulfated alkanes and sterols present in S. cf. horrens bear similarity to known kairomones and other signaling molecules. All in all, the results provide a baseline metabolomic profile of S. cf. horrens that may further be used for comparative and exploratory studies and suggest the untapped potential of S. cf. horrens as a source of bioactive molecules.
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Affiliation(s)
| | | | - Hiyas A. Junio
- Institute of Chemistry, University of the Philippines, Diliman, Quezon City, Philippines
| | - Eizadora T. Yu
- The Marine Science Institute, University of the Philippines, Diliman, Quezon City, Philippines
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Beyer TA, Sadler JE, Rearick JI, Paulson JC, Hill RL. Glycosyltransferases and their use in assessing oligosaccharide structure and structure-function relationships. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 52:23-175. [PMID: 6784450 DOI: 10.1002/9780470122976.ch2] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Gornati R, Basu S, Bernardini G, Rizzo AM, Rossi F, Berra B. Activities of glycolipid glycosyltransferases and sialidases during the early development of Xenopus laevis. Mol Cell Biochem 1997; 166:117-24. [PMID: 9046028 DOI: 10.1023/a:1006891414663] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The activities of glycosyltransferases and sialidases, together with the ganglioside content and distribution, have been extensively studied in mammals, while the informations on tissues of other animals, including amphibian, are scarce. In this paper we present data on the activities of SAT-1, SAT-2, SAT-4, SAT-5, GlcNAcT-1, GalNAcT-1, GalT-6, and sialidases studied in Xenopus laevis embryos at different stages of development. The highest activity was found at days 4 and 5 of embryogenesis for glycosyltransferases and sialidases respectively; a tentative correlation between the in vitro activity of these enzymes and the content of neutral and acidic glycolipids is discussed.
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Affiliation(s)
- R Gornati
- Institute of General Physiology and Biochemistry, University of Milan, Italy
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Critchfield JW, Carl GF, Keen CL. The influence of manganese supplementation on seizure onset and severity, and brain monoamines in the genetically epilepsy prone rat. Epilepsy Res 1993; 14:3-10. [PMID: 8095451 DOI: 10.1016/0920-1211(93)90069-j] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Human and experimental animal studies suggest a relationship between low Mn status and seizures. The genetically epilepsy prone rat (GEPR), which has low tissue Mn levels, was studied in the context of Mn supplementation. Manganese was provided at 45 micrograms/g diet (control) or 1000 micrograms/g diet (supplemented) to dams during pregnancy and lactation, then to the offspring after weaning. Offspring were tested for seizure susceptibility as young adults; tissue trace elements, brain monoamines and brain glutamine synthetase activity were measured as endpoint biochemical indices. Supplementation, although developmentally encompassing and highly effective in elevating tissue Mn levels, had no effect on seizure latency or severity. Similarly, brain monoamine concentrations and glutamine synthetase activities were resistant to Mn supplementation. Notably, the GEPR was confirmed to have low whole brain glutamine synthetase activity. These findings suggest that seizure activity in the GEPR does not stem from an increased nutritional/metabolic need for Mn.
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Affiliation(s)
- J W Critchfield
- Department of Nutrition, University of California, Davis 95616
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Abstract
As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)
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Papavasiliou PS, Miller ST. Generalized seizures alter the cerebral and peripheral metabolism of essential metals in mice. Exp Neurol 1983; 82:223-36. [PMID: 6628611 DOI: 10.1016/0014-4886(83)90257-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The effects of seizures on the cerebral and peripheral metabolism of essential metals were studied in mice. Acute and chronic seizures were produced either by electroshock (ES) or by a systemic convulsant. Organ and subcellular distribution of 54Mn and 65Zn were determined prior to and at different intervals after seizure cessation. In mice shocked for 21 days, the concentrations of manganese, zinc, magnesium, and copper were determined in selected tissues. Sham-seizured mice served as controls. When 54Mn was injected after a single ES, the isotope's retention increased in the liver by 67% (P less than 0.01) and decreased in the brain and carcass by 53 and 42%, respectively (P less than 0.01). Repeated ES further augmented these effects (P less than 0.01). These changes diminished as a function of time to the animal's recovery from ES. Liver and regional brain fractionations revealed significant perturbation in the intercellular partition of 54Mn, suggesting increased metal utilization. Brain and liver 65Zn were not affected by ES. Manganese content increased in the liver by 67% (P less than 0.01) and decreased in whole brain by 16.5% (P less than 0.01), after chronic ES. Cortical manganese and hypothalamic magnesium were the principal sites of loss. Small (12 to 13%), but significant elevations of magnesium were found in liver and skeletal muscle (P less than 0.05). Copper increased in muscle by 26% (P less than 0.02). Seizures selectively altered the normal brain and extracerebral distribution of essential metals which may lead to regional metal deficiency or excess. These changes were linked to the metabolic consequences of convulsive activity and may be relevant to seizure control and electroshock therapy in man.
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Kaplan F, Hechtman P. Purification and properties of two enzymes catalyzing galactose transfer to GM2 ganglioside from rat liver Golgi. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)33115-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Abstract
Galactosyltransferase activities were examined in the cerebellum, cerebral cortex, and brain stem of reeler and wild-type mice. Galactosyltransferase assays were optimal for all required substrates, linear with incubation time, and proportional to protein concentration. In brain areas affected by the reeler mutation (i.e., cerebral cortex and cerebellum), galactosylation of both endogenous and exogenous glycoprotein acceptors was greatly reduced in reeler relative to controls. On the other hand, glycosylation of endogenous glycolipids was low, and equal between reeler and wild-type. Galactosyltransferase activities were similar, though not identical, in reeler and wild-type brain stems, which are phenotypically normal in reeler mice. Glucosyltransferase, beta-galactosidase, beta-N-acetylglucosaminidase, acid phosphatase, and lactate dehydrogenase specific activities were all unaffected in reeler cerebella, while galactosyltransferase activity was 52% of control. Inhibition of either UDPgalactose hydrolysis or beta-galactosidase had no effect on galactosyltransferase activity. The spectrum or galactosyltransferase deficiencies in reeler suggests that this enzyme is associated with the development of young granule cells.
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Yip MC, Nguyen NT. The enzymic synthesis of GM1b: rat-brain CMP-N-acetylneuraminic acid: asialo-GM1 sialyltransferase. Lipids 1981; 16:72-6. [PMID: 7219083 DOI: 10.1007/bf02534925] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
An enzyme which catalyzes the transfer of N-acetylneuraminic acid (NeuNAc) to a tetrahexosylceramide (asialo-GM1) in young rat brain is described. The enzymic product is a new monosialoganglioside containing a neuraminidase-labile neuraminic acid, GM1b. The activity of this sialyltransferase is higher in fetal and young rat brains. The enzyme exhibits a pH optimum of 6.5 in cacodylate buffer. The incorporation of radioactivity into GM1b is stimulated in the presence of asialo-GM1 and CMP-NeuNAc and is dependent on the quantity added. The detergent mixture, Tween 80 and CF54, is required for optimal activity. Recent demonstration of the natural occurrence of GM1b in the free cell types of rat ascites hepatopa cells suggests a functional importance of this CMP-Neu-NAc:asialo-GM1 sialyltransferase in the in vivo formation of this novel monosialoganglioside.
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Basu S, Basu M, Chien JL, Presper KA. Biosynthesis of gangliosides in tissues. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1980; 125:213-26. [PMID: 6767343 DOI: 10.1007/978-1-4684-7844-0_21] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Horowitz AJ, Schanberg SM. Hormonal effects on the development of rat brain gangliosides--I. Cortisol. Biochem Pharmacol 1979; 28:881-95. [PMID: 454486 DOI: 10.1016/0006-2952(79)90372-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Distribution of ganglioside synthetizing enzymes in rat brain: Increased activity of galactosyl but not galactosaminyl transferase in the adult olfactory bulbs. Neurosci Lett 1978; 10:323-7. [DOI: 10.1016/0304-3940(78)90247-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/1978] [Revised: 10/03/1978] [Accepted: 10/06/1978] [Indexed: 11/21/2022]
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Richardson CL, Keenan TW, Morre DJ. Ganglioside biosynthesis. Characterization of CMP-N-acetylneuraminic acid : lactosylceramide sialyltransferase in Golgi apparatus from rat liver. BIOCHIMICA ET BIOPHYSICA ACTA 1977; 488:88-96. [PMID: 19080 DOI: 10.1016/0005-2760(77)90125-4] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
An enzyme that transfers sialic acid from GMP-sialic acid to lactosylceramide was concentrated 40-50 times in Golgi apparatus from rat liver relative to total homogenates. This enzyme required detergents as dispersing agents. Of the numerous detergents tested, the combination Tween 80-Triton CF-54 (1 : 2, w/w) was the most effective in stimulating the reaction. Two apparent pH optima, at 6.35 and 5.5, were observed. The enzyme showed no requirement for a divalent cation. The Km values calculated for CMP-N-acetylneuraminic acid and lactosylceramide were 2.7 - 10(-3) and 1.3 - 10(-4) M, respectively. The enzyme could not be dissociated from Golgi apparatus fractions by treatment with ultrasound, indicating that it is tightly associated with the membrane. The newly synthesized GM3, the product of the reaction, was incorporated into or became tightly associated with the membranes of the Golgi apparatus.
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Abstract
Gangliosides are unique acidic glycolipids that are selectively concentrated in the plasma membrane of cells. Surface labeling studies have demonstrated that at least a portion of the oligosaccharde chain of gangliosides extends beyond the hydrophe) is imbedded in the membrane bilayer. It is becoming increasingly apparent that gangliosides participate in the internalization of environmental signals elicited by cholera toxin and glycoprotein hormones such as thyrotropic hormone and chorionic gonadotropin as well as other substances such as interferon and possibly serotonin. The mechanism by which cholera toxin binds to a specific ganglioside receptor on the celraction of trophic agents with gangliosides. We would predict that analyogous phenomena involving gangliosides will be discovered in brain. The biosynthesis of gangliosides proceeds by the ordered sequential addition of sugars to the lipid moiety. These reactions are catalyzed by a cluster of membrane-bound glycosyltransferases. Any alteration in the activity or specificity of one of these enzymes will result in a dramatic change in the ganglioside pattern of an afflicted cell or organ. The drastic consequences that accompany abnormalities of ganglioside synthesis have been documented in a heritable metabolic disorder in vivo and in tumorigenic transformation of cells in vitro. In this article, we have attempted to unify these observations and to provide a reasonable interpretation of the role of gangliosides in mediating cell surface phenomena.
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Wilkinson FE, Morré DJ, Keenan TW. Ganglioside biosynthesis. Characterization of uridine diphosphate galactose: GM2 galactosyltransferase in Golgiapparatus from rat liver. J Lipid Res 1976. [DOI: 10.1016/s0022-2275(20)36999-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Shah SN. UDP-glucose: ceramide glucosyltransferase of rat brain: an association with smooth microsomes and requirement of an intact membrane for enzyme activity. Arch Biochem Biophys 1973; 159:143-50. [PMID: 4784456 DOI: 10.1016/0003-9861(73)90438-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
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Yip MC. A novel monosialoganglioside synthesized by a rat brain cytidine-5'-monophospho-N-acetylneuraminic acid: galactosyl-N-acetylgalactosaminyl-galactosyl-glucosylceramide sialyltransferase. Biochem Biophys Res Commun 1973; 53:737-44. [PMID: 4354446 DOI: 10.1016/0006-291x(73)90155-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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The enzymic synthesis of disialogangleoside: Rat brain cytidine-5′-monophospho-N-acetylneuramjnic acid: Monosialoganglioside (GM1) sialyltransferase. ACTA ACUST UNITED AC 1973. [DOI: 10.1016/0005-2760(73)90235-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Yip MC. The enzymic synthesis of gangliosides: uridine diphosphate galactose: N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosyl-glucosyl-ceramide galactosyltransferase in rat tissues. BIOCHIMICA ET BIOPHYSICA ACTA 1972; 273:374-9. [PMID: 5080324 DOI: 10.1016/0304-4165(72)90229-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Keenan TW, Huang CM, Morré DJ. Gangliosides: nonspecific localization in the surface membranes of bovine mammary gland and rat liver. Biochem Biophys Res Commun 1972; 47:1277-83. [PMID: 5040234 DOI: 10.1016/0006-291x(72)90211-2] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Sukeno T, Herp A, Pigman W. Enzymic characterization of Golgi-rich fractions from rat submaxillary-sublingual glands. EUROPEAN JOURNAL OF BIOCHEMISTRY 1972; 27:419-24. [PMID: 5065741 DOI: 10.1111/j.1432-1033.1972.tb01854.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Cumar FA, Tallman JF, Brady RO. The Biosynthesis of a Disialylganglioside by Galactosyltransferase from Rat Brain Tissue. J Biol Chem 1972. [DOI: 10.1016/s0021-9258(19)45432-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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DiCesare JL, Dain JA. Localization, solubilization and properties of N-acetylgalactosaminyl and galactosyl ganglioside transferases in rat brain. J Neurochem 1972; 19:403-10. [PMID: 5010086 DOI: 10.1111/j.1471-4159.1972.tb01350.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Effect of Maternal Protein Deficiency on Ganglioside Metabolism in Neonatal Rat Brain. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1972. [DOI: 10.1007/978-1-4757-6570-0_39] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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Cumar F, Fishman PH, Brady RO. Analogous Reactions for the Biosynthesis of Monosialo- and Disialo-gangliosides in Brain. J Biol Chem 1971. [DOI: 10.1016/s0021-9258(18)61971-4] [Citation(s) in RCA: 71] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Nikaido H, Hassid W. Biosynthesis of Saccharides From Glycopyranosyl Esters of Nucleoside Pyrophosphates “Sugar Nucleotides”. Adv Carbohydr Chem Biochem 1971. [DOI: 10.1016/s0065-2318(08)60371-6] [Citation(s) in RCA: 46] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Tettamanti G. Brain Gangliosides in Development. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1971. [DOI: 10.1007/978-1-4684-7236-3_7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/21/2023]
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WIEGANDT HERBERT. Glycosphingolipids1 1The survey of the literature pertaining to this review was essentially concluded in May 1970. The nomenclature is mostly in accordance with the tentative rules of the IUPAC-IUB commission. ADVANCES IN LIPID RESEARCH 1971. [DOI: 10.1016/b978-0-12-024909-1.50012-0] [Citation(s) in RCA: 106] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Yip MC, Dain JA. Frog brain uridine diphosphate galactose-N-acetylgalactosaminyl-N-acetylneuraminylgalactosylglucosylceramide galactosyltransferase. Biochem J 1970; 118:247-52. [PMID: 5484669 PMCID: PMC1179110 DOI: 10.1042/bj1180247] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
1. The enzyme that catalyses the transfer of galactose from UDP-galactose to N-acetylgalactosaminyl-(1-->4)-N-acetylneuraminyl-(2-->3)-galactosyl-(1-->4)-glucosylceramide (G(M2)) was found mainly in the heavy- and light-microsomal fractions of the adult frog brain. 2. The subcellular distribution of the enzyme, UDP-galactose-G(M2) galactosyltransferase, parallels that of gangliosides in adult frog brain. 3. The enzymic activity was first detected at late gastrulation (Shumway stage 11(1/2)) and increased until the completion of the operculum (Shumway stage 25) and then decreased in the tadpoles. 4. In adult frog brain, the enzyme exhibited a pH optimum of 7.2-7.3 in both cacodylate and tris buffers. The enzyme required 10mm-Mn(2+) for maximal activity and the K(m) for Mn(2+) was determined as 2.2mm. The half-maximal velocity was obtained at a G(M2) concentration of 0.18mm. Inhibition of the enzymic reaction was found when the G(M2) concentration was greater than 1.38mm. 5. The enzymic activity was also inhibited by the products in the pathway of ganglioside synthesis, i.e. either by a mixture of gangliosides or by individual ganglioside components. The most active inhibitor was disialoganglioside. The degree of inhibition is a function of the individual ganglioside concentration. 6. A product-inhibition mechanism for the regulation of ganglioside biosynthesis is discussed.
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