- Library Home /
- Search Collections /
- Open Collections /
- Browse Collections /
- UBC Theses and Dissertations /
- The biomethylation of arsenic
Open Collections
UBC Theses and Dissertations
UBC Theses and Dissertations
The biomethylation of arsenic Li, Hao
Abstract
A semi-continuous hydride generation-gas chromatography-atomic absorption spectrometry (HG-GC-AA) system was developed and optimized for the determination of arsenite, arsenate, methylarsonate (MMA), dimethylarsinate (DMA), and trimethylarsine oxide (TMAO). Particularly, this system was used to study the pathway for the biomethylation of arsenicals in microorganisms and a marine alga. The HG-GC-AA system was used to separate and identify the extracellular arsenic metabolites produced by the microorganisms Apiotrichum humicola (previously known as Candida humicola) and Scopulariopsis brevicaulis growing in the liquid medium enriched with arsenicals. Arsenite, MMA, DMA, and TMAO were detected following incubation with arsenate. With arsenite as a substrate, the metabolites were MMA, DMA, and TMAO; MMA afforded DMA and TMAO, and DMA afforded TMAO. Trimethylarsine was not detected in these investigations. The production of the anticipated methylated intermediates from the substrates strongly support the metabolic sequence proposed by Challenger (Challenger, F Chem. Rev., 1945, 36:315). When L3-methionine-methyl-d₃ was added to the growing culture of Apiotrichum humicola grown in the presence of either arsenate, arsenite, MMA, or DMA, the CD₃ label was incorporated intact into the arsenic metabolites (DMA and TMAO) to a considerable extent, indicating that S-adenosylmethionine (SAM), or some related suiphonium compound, is involved in the biological methylation. Conclusive evidence of CD₃ incorporation into the arsenicals was provided by using a specially developed hydride generation-gas chromatography-mass spectrometry methodology (HG-GC-MS). When a unicellular marine alga Polyphysa peniculus was grown in artificial seawater enriched with arsenicals, the arsenic metabolites produced in the cells as well as in the growth medium were identified by using HG-GC-AA methodology. Arsenite and DMA were detected following incubation with arsenate. When the alga was treated with arsenite, DMA was the major metabolite in the cells and in the growth medium; trace amounts of MMA were also detected in the cells. With methylarsonate as a substrate, the metabolite was dimethylarsinate. Polyphysa peniculus did not metabolize dimethylarsinic acid when it was used as a substrate. Significant amounts of more complex arsenic species, such as arsenosugars, were not observed in the cells or medium based on the evidence given by flow injection-microwave digestion-hydride generationatomic absorption spectrometry methodology. Transfer of the exposed cells to fresh medium caused release of most cell associated arsenicals to the surrounding environment. The alga seems to follow the biomethylation pathway proposed by Challenger for microbial process, and in the case of P. peniculus, DMA is the end product of this biomethylation. When L-methionine-methyl-d₃ was added to the culture of Polyphysa peniculus enriched with 1 ppm of arsenate, the CD₃ label was incorporated intact in the DMA metabolite to a considerable extent. It thus confirmed that P. peniculus also follows the oxidation-reduction pathway involving carbonium ions originally suggested by Challenger for the alkylation of arsenic by microorganisms. The HG-GC-MS system was also used to identify the antimony hydrides produced from the trimethylantimony compoundsMe₃Sb(OH)₂ and Me₃SbCl₂.The possible causes of the molecular rearrangement of trimethyistibine were investigated. The extracts of plant samples collected from Kam Lake and Keg Lake (Yellowknife) were analyzed by using the HG-GC-MS system. The results provided conclusive evidence of the presence of methylantimony compounds in these samples.
Item Metadata
Title |
The biomethylation of arsenic
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
1994
|
Description |
A semi-continuous hydride generation-gas chromatography-atomic absorption
spectrometry (HG-GC-AA) system was developed and optimized for the determination
of arsenite, arsenate, methylarsonate (MMA), dimethylarsinate (DMA), and
trimethylarsine oxide (TMAO). Particularly, this system was used to study the pathway
for the biomethylation of arsenicals in microorganisms and a marine alga.
The HG-GC-AA system was used to separate and identify the extracellular
arsenic metabolites produced by the microorganisms Apiotrichum humicola (previously
known as Candida humicola) and Scopulariopsis brevicaulis growing in the liquid
medium enriched with arsenicals. Arsenite, MMA, DMA, and TMAO were detected
following incubation with arsenate. With arsenite as a substrate, the metabolites were
MMA, DMA, and TMAO; MMA afforded DMA and TMAO, and DMA afforded
TMAO. Trimethylarsine was not detected in these investigations. The production of the
anticipated methylated intermediates from the substrates strongly support the metabolic
sequence proposed by Challenger (Challenger, F Chem. Rev., 1945, 36:315).
When L3-methionine-methyl-d₃ was added to the growing culture of Apiotrichum
humicola grown in the presence of either arsenate, arsenite, MMA, or DMA, the CD₃
label was incorporated intact into the arsenic metabolites (DMA and TMAO) to a
considerable extent, indicating that S-adenosylmethionine (SAM), or some related
suiphonium compound, is involved in the biological methylation. Conclusive evidence of
CD₃ incorporation into the arsenicals was provided by using a specially developed
hydride generation-gas chromatography-mass spectrometry methodology (HG-GC-MS).
When a unicellular marine alga Polyphysa peniculus was grown in artificial
seawater enriched with arsenicals, the arsenic metabolites produced in the cells as well
as in the growth medium were identified by using HG-GC-AA methodology. Arsenite
and DMA were detected following incubation with arsenate. When the alga was treated
with arsenite, DMA was the major metabolite in the cells and in the growth medium;
trace amounts of MMA were also detected in the cells. With methylarsonate as a
substrate, the metabolite was dimethylarsinate. Polyphysa peniculus did not metabolize
dimethylarsinic acid when it was used as a substrate. Significant amounts of more
complex arsenic species, such as arsenosugars, were not observed in the cells or medium
based on the evidence given by flow injection-microwave digestion-hydride generationatomic
absorption spectrometry methodology. Transfer of the exposed cells to fresh
medium caused release of most cell associated arsenicals to the surrounding
environment. The alga seems to follow the biomethylation pathway proposed by
Challenger for microbial process, and in the case of P. peniculus, DMA is the end
product of this biomethylation.
When L-methionine-methyl-d₃ was added to the culture of Polyphysa peniculus
enriched with 1 ppm of arsenate, the CD₃ label was incorporated intact in the DMA
metabolite to a considerable extent. It thus confirmed that P. peniculus also follows the
oxidation-reduction pathway involving carbonium ions originally suggested by
Challenger for the alkylation of arsenic by microorganisms.
The HG-GC-MS system was also used to identify the antimony hydrides
produced from the trimethylantimony compoundsMe₃Sb(OH)₂ and Me₃SbCl₂.The
possible causes of the molecular rearrangement of trimethyistibine were investigated.
The extracts of plant samples collected from Kam Lake and Keg Lake (Yellowknife)
were analyzed by using the HG-GC-MS system. The results provided conclusive
evidence of the presence of methylantimony compounds in these samples.
|
Extent |
4484578 bytes
|
Genre | |
Type | |
File Format |
application/pdf
|
Language |
eng
|
Date Available |
2009-04-07
|
Provider |
Vancouver : University of British Columbia Library
|
Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
|
DOI |
10.14288/1.0059605
|
URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Graduation Date |
1994-11
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
|
Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.