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J K MacLeod

Publications and source records attributed to J K MacLeod.

At least 19 recordsLinked to original sources
PubMed2001

Mild tagging procedures for the structural analysis of glycans.

The reductive oxyamination of model glycan structures has been investigated as a mild, alternative tagging procedure to reductive amination using O-(4-nitrobenzyl)-hydroxylamine. Oxime formation was quantitative, but the reduction step did not always go to completion. Novel O- and N-substituted 7-hydroxycoumaryl- and 3-methoxybenzylhydroxylamines were synthesized and shown to couple quantitatively with model saccharides by oxime formation and reductive hydroxyamination, respectively, under very mild, aqueous conditions. The fluorescent derivatives produced show good chromatographic and mass spectrometric properties. Both procedures are suitable for the labeling of carbohydrates and oligosaccharide fragments from glycosaminoglycan structures, such as heparin and heparan sulfate.

Chromatography, High Pressure Liquid↗
PubMed2001

Mass spectrometric studies of the path of carbon in photosynthesis: positional isotopic analysis of (13)C-labelled C(4) to C(7) sugar phosphates.

The (EIMS) electron ionization mass spectrometric fragmentation patterns of the methoxime- and ethoxime-trimethylsilyl (TMS) derivatives of C(4) to C(7) sugars involved as phosphates in the Calvin pathway of photosynthesis in plants were analysed by gas chromatography/EIMS using specifically labelled (13)C analogs. In general, most but not all of the major ions in the mass spectra arise from single carbon-carbon bond cleavages of the straight-chain derivatives. The results confirm that GC/MS of the alkoxime-TMS derivatives is a viable method for measuring (13)C incorporations at individual carbon atoms in each of the sugar phosphates during photosynthetic experiments with (13)CO(2).

Carbon↗
PubMed2001

Isolation and identification of the toxic peptides from Lophyrotoma zonalis (Pergidae) sawfly larvae.

The broad-leaved paper bark tree Melaleuca quinquenervia (Cav) (Myrtaceae) was introduced into Florida (USA) early in this century it has proliferated to such an extent that urgent measures are now required to control it. The sawfly Lophyrotoma zonalis (Pergidae) has been introduced as a possible biological control agent due to its ability to defoliate M. quinquenervia. Because toxic D-amino acid- containing peptides have been isolated from some sawfly species, L. zonalis larvae were processed using the previously reported method for the recovery of these compounds. The toxins lophyrotomin (as the free C-terminal acid) and a mixture of pergidin and Val (4)-pergidin were isolated at 0.36 and 0.43% yield of the dried larvae, respectively. Both compounds when dosed intraperitoneally to C57/Bl6 male mice were hepatotoxic with lowest lethal doses of 8 and 32 mg/kg, respectively. The pathology of the liver was different for each compound, with the lophyrotomin free acid causing a periportal haemorrhagic necrosis and the pergidin causing a periacinar coagulative necrosis.

Animals↗
PubMed2001

Two new lactones with mosquito larvicidal activity from three Hortonia species.

The structures of the butenolides 1 and 2, isolated from the endemic plants Hortonia floribunda, H. angustifolia, and H. ovalifolia, collected in Sri Lanka, have been elucidated by spectroscopic analysis. These compounds exhibited potent mosquito larvicidal activity against the second instar larvae of Aedes aegypti.

Aedes↗
PubMed1999

Unique toxic peptides isolated from sawfly larvae in three continents.

D-Amino acid containing peptides have been found to be responsible for sawfly larvae poisoning in many parts of the world. These compounds, unique in the animal kingdom, were isolated from three different species of sawfly indigenous to Australia, Denmark and South America. The octapeptide, lophyrotomin, is the major toxin in the Australian and Danish species and is present in small amounts in the South American sawfly. Pergidin, the main toxin in the South American sawfly, is a heptapeptide containing a phosphoseryl residue. This, as far as we are aware, is the first example of such a peptide to be isolated from an animal source. Small amounts of pergidin have been found in the other two species. All available evidence suggests that both peptides are biosynthesised 'de novo' possibly as a protective device, however it cannot be excluded that microorganisms may be responsible. These compounds are stable to enzymatic breakdown because of their configuration and their strong chemical bonding and lipophilic character provide a potential for residues to remain in the host animal and cause significant changes.

Animals↗
PubMed1997

Structural investigation of resin glycosides from Ipomoea lonchophylla.

A fraction from Ipomoea lonchophylla, which was toxic to mice, contained an inseparable mixture of resin glycosides with differing numbers of C5 ester groups on the hexasaccharide chain. After alkaline hydrolysis of the esters, the structure of the major component (1) was elucidated using high-field NMR spectroscopy, mass spectrometry, chemical studies, and comparison with known resin glycosides. Compound 1 was identified as 3,11-dihydroxytetradecanoic acid 11-O-beta-quinovopyranosyl-(1-->2)-beta-glucopyranosyl-(1-->3)- [alpha-rhamnopyranosyl- (1-->4)]-quinovopyranosyl-(1-->2)-beta-glucopyranosyl-(1-->2)-beta -fucopyranoside.

Animals↗
PubMed1995

Kinetic characteristics of rat liver peroxisomal nafenopin-CoA ligase.

In this study we have demonstrated that rat hepatic peroxisomes catalyse the formation of nafenopin-CoA. The process is mediated by apparent high affinity (Km 6.7 microM), low capacity (Vmax 0.31 nmol/mg/min) and low affinity, high capacity isoforms. Palmitic acid (Ki 1.1 microM), R(-) ibuprofen (Ki 7.9 microM), ciprofibrate (Ki 60.2 microM) and clofibric acid (Ki 86.8 microM) competitively inhibited nafenopin-CoA formation catalysed by the apparent high affinity isoform. An antibody raised against the microsomal palmitoyl-CoA ligase inhibited the equivalent peroxisomal enzyme significantly (P < 0.001) but did not inhibit peroxisomal nafenopin-CoA ligase activity. These data suggest that nafenopin-CoA formation is catalysed by a peroxisomal CoA ligase which differs from the peroxisomal long chain fatty acid-CoA ligase in relation to its xenobiotic/antibody inhibitor profile and kinetic characteristics.

Animals↗
PubMed1995

Isolation and identification of a compound from avocado (Persea americana) leaves which causes necrosis of the acinar epithelium of the lactating mammary gland and the myocardium.

It is well known that when lactating livestock eat avocado (Persea americana) leaves they may develop non-infectious mastitis and agalactia. This is associated with extensive coagulation necrosis of the secretory acinar epithelium and interstitial oedema, congestion, and haemorrhage. Similar lesions have been produced in mammary glands of lactating mice fed a diet containing a small percentage of freeze-dried avocado leaf. Tests using these animals have been used to isolate the active principle, termed "persin," from avocado leaves. The purified persin was examined using IR, NMR, and UV spectroscopy and mass spectrometry, and identified as (Z,Z)-1-(acetyloxy)-2-hydroxy-12,15-heneicosadien-4-one. Persin has previously been isolated from avocado leaves and shown to have antifungal properties and to be toxic to silkworms. Our tests have shown that persin at the dose rate of 60-100 mg/kg has the same effect on mammary glands in lactating mice as leaves from avocado. Enantioselective syntheses of the R and the S isomers of persin and related derivatives were carried out. These compounds were tested for activity required to induce widespread lactating mammary gland necrosis in mice, and only the R isomer was found active. At doses of persin above 100 mg/kg necrosis of myocardial fibres may occur and hydrothorax may be present in severely affected animals. The mechanism of action of persin on both the mammary gland and the myocardium remain to be resolved.

Animals↗
PubMed1995

Isolation of a compound from Eupatorium adenophorum (Spreng.) [Ageratina adenophora (Spreng.)] causing hepatotoxicity in mice.

Regular ingestion of Eupatorium adenophorum [Ageratina adenophora (Spreng.)] or Crofton weed causes chronic pulmonary disease in horses mainly in Australia, New Zealand, and the Himalayas. The disease is characterized by pulmonary interstitial fibrosis, emphysema, alveolar epithelisation and reduced tolerance to exercise. Horses apparently are the only animals affected and there are numerous reports of farms losing all their horses. The disorder was produced experimentally in horse feeding trials, and it was shown that characteristic lesions occurred in the lungs. In studies with laboratory animals, mice were shown to be suitable test animals, but in this species lesions occur in the liver rather than the lungs. The hepatic injury in these animals is characterized by multiple areas of focal necrosis of the parenchyma associated with degeneration and loss of the epithelium lining the small bile ducts. The active principle 9-oxo-10,11 dehydroagerophorone responsible for these lesions in mice has been isolated from E. adenophorum. Although the compound has been shown to exhibit toxicity to larvae of invertebrate species, no mammalian toxicity studies have been previously reported involving the isolated toxin. The mechanism of the toxic effect of the compound as well as its possible relevance to the respiratory disease in the horse remain to be investigated.

Administration, Oral↗
PubMed1993

Exchange reactions catalyzed by group-transferring enzymes oppose the quantitation and the unravelling of the identify of the pentose pathway.

1. The distributions and rates of transfer of carbon isotopes from a selection of specifically labelled ketosugar-phosphate substrates by exchange reactions catalyzed by the pentose and photosynthetic carbon-reduction-pathway group-transferring enzymes transketolase, transaldolase and aldolase have been measured using 13C-NMR spectroscopy. 2. The rates of these exchange reactions were 5, 4 and 1.5 mumol min-1 mg-1 for transketolase exchange, transaldolase exchange and aldolase exchange, respectively. 3. A comparison of the exchange capacities contributed by the activities of these enzymes in three in vitro liver preparations with the maximum non-oxidative pentose pathway flux rates of the preparations shows that transketolase and aldolase exchanges exceeded flux by 9-19 times in liver cytosol and acetone powder enzyme preparations and by 5 times in hepatocytes. Transaldolase was less effective in the comparison of exchange versus flux rates: transaldolase exchange exceeded flux by 1.6 and 5 in catalysis by liver cytosol and acetone powder preparations, respectively, but was only 0.6 times the flux in hepatocytes. 4. Values of group enzyme exchange and pathway flux rates in the above three preparations are important because of the feature role of liver and of these particular preparations in the establishment, elucidation and measurement of a proposed reaction scheme for the fat-cell-type pentose pathway in biochemistry. 5. It is the claim of this paper that the excess of exchange rate activity (particularly transketolase exchange) over pathway flux will overturn attempts to unravel, using isotopically labelled sugar substrates, the identity, reaction sequence and quantitative contribution of the pentose pathway to glucose metabolism. 6. The transketolase exchange reactions relative to the pentose pathway flux rates in normal, regenerating and foetal liver, Morris hepatomas, mammary carcinoma, melanoma, colonic epithelium, spinach chloroplasts and epididymal fat tissue show that transketolase exchange may exceed flux in these tissues by factors ranging over 5-600 times. 7. The confusion of pentose pathway theory by the effects of transketolase exchange action is illustrated by the 13C-NMR spectrum of the hexose 6-phosphate products of ribose 5-phosphate dissimilation, formed after 30 min of liver enzyme action, and shows 13C-labelling in carbons 1 and 3 of glucose 6-phosphate with ratios which range over 2.1-6.4 rather than the mandatory value of 2 which is imposed by the theoretical mechanism of the pathway.

Animals↗
PubMed1991

Purification and characterization of ciguatoxins from moray eel (Lycodontis javanicus, Muraenidae).

Viscera (48.3 kg) from moray eels (Lycodontis javanicus) collected in a ciguatera endemic area were extracted and the ciguatoxins characterized. Three major ciguatoxins, CTX-1, CTX-2 and CTX-3, were isolated and purified to homogeneity on reverse phase high performance liquid chromatography. Several minor toxins were also detected. CTX-1 (490 micrograms) was comparable by both 1H nuclear magnetic resonance (1H NMR) and mass spectroscopy (MH+ m/z = 1111) to ciguatoxin isolated previously from moray eels. CTX-2 (280 micrograms) and CTX-3 (100 micrograms) were less polar ciguatoxins not previously characterized. CTX-2 and CTX-3 differed from CTX-1 by 16 mass units, suggesting that they were less oxygenated analogues. 1H NMR revealed that the hydroxyl at C54 in CTX-1 was absent in CTX-2 and CTX-3. An additional change in the chemistry of CTX-2 compared to CTX-1 and CTX-3 was also suggested on the basis of 1H NMR, indicating that CTX-2 may arise from a different precursor to CTX-1. CTX-3 is likely to be an intermediate in the oxidation of a gambiertoxin (sodium channel toxins from Gambierdiscus toxicus) to CTX-1. The i.p. LD50 values for CTX-1, CTX-2 and CTX-3 were 0.25, 2.3 and 0.9 micrograms/kg, respectively. The signs induced in mice by the ciguatoxins were similar, except that CTX-2 and CTX-3 induced hind-limb paralysis that was absent with CTX-1. Each ciguatoxin was potent orally. CTX-1, CTX-2 and CTX-3 competitively inhibited the binding of [3H]brevetoxin-3 to voltage-dependent sodium channels with relative potencies qualitatively (but not quantitatively) comparable to mouse lethality. This study reveals that the relatively small chemical differences between CTX-1, CTX-2 and CTX-3 give rise to significant structure-activity and pharmacokinetic differences.

Animals↗
PubMed1988

Rapid methods for the high yield synthesis of carbon-13 enriched intermediates of the pentose-phosphate pathway.

Methods for the synthesis of carbon-13 enriched substrates, intermediates and products of the pentose-phosphate pathway, viz. ribose, arabinose, xylulose and ribulose 5-phosphates, sedoheptulose mono- and bisphosphates, octulose (both the ido- and altro-epimers) mono- and bisphosphates, are described. The procedure of the classical Kiliani synthesis was adopted for the preparation of the two starting compounds, [1-13C]ribose and [1-13C]arabinose 5-phosphates. Using these initial reactants and enzymic methods involving the group-transferring enzymes, transketolase, aldolase and transaldolase, a variety of specifically 13C-labelled five-, six-, seven- and eight-carbon sugar phosphates were synthesized in high yield and purity. The isolation and authenticity of each of the 13C-labelled sugars were established by column, paper and thin layer chromatographic methods and specific enzymic assays. The purity and positional isotopic analysis of these sugar-P's were confirmed by 13C-NMR spectroscopy. These specifically 13C-enriched compounds are required for enzymatic, mechanistic and quantitative investigations of pentose-pathway reactions in animal, plant and tumour tissues in vitro and in vivo.

Carbon Isotopes↗
PubMed1986

Mass spectrometry and chromatography of t-butyldimethylsilyl derivatives of cytokinin bases.

Di-(t-butyldimethylsilyl) derivatives of the cytokinin bases zeatin, cis-zeatin, and dihydrozeatin may be prepared quantitatively in the presence of dimethylaminopyridine. These derivatives have good gas chromatographic properties and are very suitable for gas chromatography-mass spectrometry analysis of cytokinin bases. The t-butyldimethylsilyl (tBuDMS) group at N-9 may be selectively hydrolyzed and the resulting mono-O-silyl derivatives are sufficiently stable to be subjected to thin-layer chromatography and high-performance liquid chromatography. The mass spectral fragmentation of the mono- and di-tBuDMS derivatives of adenine, zeatin, cis-zeatin, and dihydrozeatin and also of the mono-tBuDMS derivatives of N6-isopentenyladenine and 6-benzylaminopurine have been rationalized. The 9-tBuDMS moiety was characterized by an elimination of isobutene (M-56) and of isobutene plus a methyl radical (M-56-15).

Chemical Phenomena↗