The arsenite methyltransferase from Nostoc sp. PCC7120 methylated trivalent antimony. In engineered E. coli, about 80 percent of 10 micromolar Sb(III) became nonvolatile methylated antimony, mostly dimethylantimony, and the methylation ratio fell to 26 percent at 100 micromolar. Purified enzyme converted about 10 percent of Sb(III) to monomethyl and dimethyl species in 20 hours. In a paddy-soil enrichment, about 12 percent of added Sb(III) was transformed to monomethyl and dimethyl species in the liquid, with trimethylantimony in the headspace.
Key numbers
Figures below are copied as printed. Units are not converted. Species are not merged.
| Analyte | What was reported | Value | Unit | Basis | Where |
|---|---|---|---|---|---|
| Sb | The reaction contained 12 μM Sb(III) and 7.5 μM purified NsArsM | 12 | μM | initial concentration | Figure 2B, p. 4 |
| Sb | adding 20 μM Sb(III) to the enrichment culture | 20 | μM | added concentration | Methods, anaerobic enrichment, p. 4 |
| Sb | the control was greatly inhibited to approximately 10% (OD600) at 200 μM Sb(III) | approximately 10% | percent of OD600 relative to uninhibited growth, as printed | culture OD600 | Figure 1A, p. 5 |
| Sb | the recombinant cells were weakly inhibited (62%) | 62% | percent remaining growth, as printed weakly inhibited (62%) | culture OD600 | Figure 1A, p. 5 |
| Sb | At 10 μM Sb(III), approximately 80% of Sb(III) was transformed to nonvolatile methylated Sb | approximately 80% | percent of Sb(III) transformed to nonvolatile methylated Sb | fraction of added Sb(III) | Figure 1B, p. 5 |
| Sb | including nearly 90% DMSb(III), 6% MMSb(III), and 4% TMSb(III) | nearly 90% | percent of methylated Sb | share of methylated Sb | Figure 1B, p. 5 |
| Sb | 6% MMSb(III) | 6% | percent of methylated Sb | share of methylated Sb | Figure 1B, p. 5 |
| Sb | 4% TMSb(III) | 4% | percent of methylated Sb | share of methylated Sb | Figure 1B, p. 5 |
| Sb | The methylation ratio decreased from 80 to 26% with increasing Sb(III) from 10 to 100 μM | 80 to 26% | percent methylation ratio | fraction methylated | Figure 1B, p. 5 |
| Sb | MMSb(III) was increased up to 17% of total Sb species and 66% of methylated Sb | 17% | percent of total Sb species | share of total Sb | Figure 1B, p. 5 |
| Sb | 66% of methylated Sb | 66% | percent of methylated Sb | share of methylated Sb | Figure 1B, p. 5 |
| Sb | DMSb(III) (6% of total and 24% of methylated Sb) | 6% | percent of total Sb | share of total Sb | Figure 1B, p. 5 |
| Sb | 24% of methylated Sb | 24% | percent of methylated Sb | share of methylated Sb | Figure 1B, p. 5 |
| Sb | Purified NsArsM protein transformed about 10% of Sb(III) to MMSb(III) and DMSb(III) after 20 h of incubation | about 10% | percent of Sb(III) | fraction of Sb(III) | Figure 2A, p. 5 |
The structured evidence record for this source holds 16 copied values. The table above is the short set.
Methods (brief)
Sb(III) was potassium antimony tartrate. Cells expressing the Nostoc gene were grown with 10 to 200 micromolar Sb(III). In vitro reactions used 7.5 micromolar enzyme, 8 mM glutathione, and 0.3 mM S-adenosylmethionine at 37 degrees C. Paddy-soil enrichments received 20 micromolar Sb(III) and were incubated 7 days. Monomethyl and dimethyl species were quantified against trimethylantimony on a semiquantitative assumption of equal hydride yield.
Evidence fitness
The Nostoc ArsM enzyme methylates Sb(III) to mono-, di-, and trimethylantimony in engineered E. coli and in vitro, and methylated Sb was detected in a paddy-soil anaerobic enrichment given Sb(III).
It does not measure antimony in drinking water, food, or consumer products. Environmental percentages in the introduction (sediment, sludge, geothermal water, seawater) are cited from earlier papers and are not copied. It does not report inorganic arsenic concentrations from these experiments.
Limitations
Monomethyl and dimethyl percentages depend on the equal-hydrogenation assumption. The oxidation state of the products could not be determined because hydride generation reduces the species. One paddy-soil enrichment is reported as approximately 12 percent, without a printed standard deviation in the text. Introduction occurrence ranges are from other studies and are excluded.
Related evidence
Update history
No substantive edit history is available in this build. The full commit record is available in git.