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H Lux

Publications and source records attributed to H Lux.

12 recordsLinked to original sources
PubMed2002

Soil warming and carbon-cycle feedbacks to the climate system.

In a decade-long soil warming experiment in a mid-latitude hardwood forest, we documented changes in soil carbon and nitrogen cycling in order to investigate the consequences of these changes for the climate system. Here we show that whereas soil warming accelerates soil organic matter decay and carbon dioxide fluxes to the atmosphere, this response is small and short-lived for a mid-latitude forest, because of the limited size of the labile soil carbon pool. We also show that warming increases the availability of mineral nitrogen to plants. Because plant growth in many mid-latitude forests is nitrogen-limited, warming has the potential to indirectly stimulate enough carbon storage in plants to at least compensate for the carbon losses from soils. Our results challenge assumptions made in some climate models that lead to projections of large long-term releases of soil carbon in response to warming of forest ecosystems.

Biodegradation, Environmental↗
PubMed2000

Ether--lipid (alkyl-phospholipid) metabolism and the mechanism of action of ether--lipid analogues in Leishmania.

Ether-lipid (alkyl-phospholipid) analogues such as Miltefosine possess potent in vitro and in vivo anti-leishmanial activity and these compounds are currently undergoing clinical trials in humans. These analogues are also effective against Trypanosoma cruzi and Trypanosoma brucei subspecies but their mode of action is not known. Leishmania have high levels of ether-lipids and these are mainly found in the glycosylphosphatidylinositol-anchored glycolipids and glycoproteins present on the surface of the parasites. In Leishmania mexicana promastigotes we have studied both the initiating steps for the biosynthesis of ether-lipids, and key remodelling steps. The effect of Miltefosine and Edelfosine, on key enzymes involved in the metabolism of ether-lipids has been studied. The enzymes include dihydroxyacetonephosphate acyltransferase, sn-l-acyl-2-lyso-glycero-3-phosphocholine and sn-l-alkyl-2-lyso-glycero-3-phosphocholine acyltransferases. We confirm that the initiating steps in ether-lipid metabolism in Leishmania are present in glycosomes, and that Miltefosine or Edelfosine did not perturb these enzymes. The metabolism of the latter phosphatidylcholine base intermediates, which may be involved in the remodelling of acyl- and alkyl-glycerophospholipids, was also seemingly associated with glycosomes. Both Miltefosine and Edelfosine inhibited this microbody (glycosomal) located alkyl-specific-acyl-CoA acyltransferase in a dose-dependent manner with an inhibitory concentration of 50 microM. It is suggested therefore that a perturbation of ether-lipid remodelling could be responsible for the anti-leishmanial action of these drugs.

Acylation↗
PubMed1997

Characterisation of phosphoglycerate kinase genes in Leishmania major and evidence for the absence of a third closely related gene or isoenzyme.

We have characterised the phosphoglycerate kinases (PGKs) in L. major and studied their mRNA and protein expression. Interestingly we have found evidence for only two tandemly linked PGK genes which correspond to the PGK gene B and C homologue in Trypanosoma and Crithidia. The primary structure of the leishmanial PGK genes B and C are virtually identical and differed only by the presence of a 62 amino acid extension at the carboxyl terminal of the PGK gene C homologue which is therefore likely to contain the translocation signal for glycosomal topogenesis. Indeed, the PGK gene C protein was found to be glycosomal (gPGK) while the PGK gene B protein was found to be cytosolic (cPGK). Both PGK genes are expressed in L. major promastigotes with the cPGK transcript expressed at a much higher level (4-5-fold) than the gPGK transcript. Similarly the relative cPGK isoenzyme activity was found to be approximately 4-fold higher than that of the gPGK isoenzyme. Surprisingly in L. major we have found no evidence for the PGK gene A present in all other trypanosomatids studied to date (Trypanosoma brucei, Trypanosoma congolense and Crithidia fasciculata). We therefore consider the possible evolutionary and functional significance of a trypanosomatid with only two PGK isoenzymes.

Amino Acid Sequence↗
PubMed1986

[Imaging of cecal tumors using computer tomography].

Although contrast enema of the colon and endoscopy remain the preferential diagnostic methods in tumour of the caecum, computed tomography can accurately determine the extent of extraluminar tumour growth and hence help to arrive preoperatively at the appropriate therapeutic concept. Adenocarcinomas are morphologically distinctly different, due to focal thickenings of the colon wall, from the diffuse wall thickenings associated with malignant lymphomas, or from inflammatory conglomerate tumours. Computed tomography of the caecal region is a noninvasive examination method that can speed up diagnosis especially in elderly patients with elongated colon and stool incontinence.

Adenocarcinoma↗