PubMed Health⌕ Search

Biomedical subjects

M R Walton

Publications and source records attributed to M R Walton.

6 recordsLinked to original sources
PubMed2001

Use of selective inhibitors and chromogenic substrates to differentiate bacteria based on toluene oxygenase activity.

In whole-cell studies, two alkynes, 1-pentyne and phenylacetylene, were selective, irreversible inhibitors of monooxygenase enzymes in catabolic pathways that permit growth of bacteria on toluene. 1-Pentyne selectively inhibited growth of Burkholderia cepacia G4 (toluene 2-monooxygenase [T2MO] pathway) and B. pickettii PKO1 (toluene 3-monooxygenase [T3MO] pathway) on toluene, but did not inhibit growth of bacteria expressing other pathways. In further studies with strain G4, chromogenic transformation of alpha,alpha,alpha-Trifluoro-m-cresol (TFC) was irreversibly inhibited by 1-pentyne, but the presence of phenol prevented this inhibition. Transformation of catechol by G4 was unaffected by 1-pentyne. With respect to the various pathways and bacteria tested, phenylacetylene selectively inhibited growth of Pseudomonas mendocina KR1 (toluene 4-monooxygenase [T4MO] pathway) on toluene, but not on p-cresol. An Escherichia coli transformant expressing T4MO transformed indole or naphthalene in chromogenic reactions, but not after exposure to phenylacetylene. The naphthalene reaction remained diminished in phenylacetylene-treated cells relative to untreated cells after phenylacetylene was removed, indicating irreversible inhibition.These techniques were used to differentiate toluene-degrading isolates from an aquifer. Based on data generated with these indicators and inhibitors, along with results from Biolog analysis for sole carbon source oxidation, the groundwater isolates were assigned to eight separate groups, some of which apparently differ in their mode of toluene catabolism.

Acetylene↗
PubMed2000

PU.1 expression in microglia.

The transcription factor PU.1 has a pivotal role in both the generation and function of macrophages. To determine whether PU.1 is also involved in microglial regulation, we investigated its expression following hypoxic-ischemia (HI) brain injury and in the BV-2 microglial cell line. We found that microglia constitutively expressed high levels of PU.1 protein in both their 'resting' and 'activated' states.

Animals↗
PubMed2000

Is CREB a key to neuronal survival?

A range of molecules control nerve-cell survival in the brain. Many of these molecules might be neuroprotective through activation of the transcription factor cAMP-response-element-binding protein (CREB). Activation of CREB, by phosphorylation of Ser133, occurs in brain-damage-resistant hippocampal dentate granule cells and is triggered by neuroprotective environmental stimulation. In addition, the Akt neuroprotective signaling pathway activates CREB, and CREB synthesis and phosphorylation promote the survival of many cells, including neurons, in vitro. Thus, CREB might be responsible for programmed nerve-cell survival. Studies investigating its role in the brain are now required to confirm these in vitro results, and the downstream survival genes, whose expression is activated by CREB in neurons, need to be identified.

Animals↗
PubMed1997

Bax expression in mammalian neurons undergoing apoptosis, and in Alzheimer's disease hippocampus.

Recent studies indicate that the proto-oncogene Bax, and other related proteins (eg Bcl-2) may play a major role in determining whether cells will undergo apoptosis under conditions which promote cell death. Increased expression of Bax has been found to promote apoptosis, while over-expression of Bcl-2 can inhibit apoptosis. To investigate the role of Bax in nerve cell death in the rat brain we examined the level of Bax expression in cells undergoing apoptosis, using a hypoxic-ischemic stroke model. We found that Bax was expressed at high levels in the nuclei of neurons in the hippocampus, cortex, cerebellum, and striatum on the control side, and that Bax levels increased in hippocampal neurons undergoing apoptosis on the stroke side, and then declined (correlating with cell loss). In the Alzheimer's disease hippocampi we found a concentrated localisation of Bax in senile plaques, which correlated with the localisation of beta-amyloid protein in adjacent sections from the same brains. beta-Amyloid positive plaques are thought to contribute to the Alzheimer's disease process, possibly via an apoptotic mechanism, and this may occur via an increase in Bax in these areas. Bax was also strongly stained in tau-positive tangles in Alzheimer's disease hippocampi, suggesting Bax may play a role in tangle formation. In addition, we observed a loss of Bax expression in the dentate granule cells of Alzheimer's disease hippocampi compared with moderate Bax expression in control hippocampi, and this loss may be related to the survival of these neurons in Alzheimer's disease. Finally, we observed substantially different staining patterns of Bax using three different commercially available antisera to Bax, indicating the need for caution when interpreting results in this area.

Adult↗