Effect of D‐amino acid contamination on isotope enrichment in plasma and urine.
Bibliographic record
Abstract
During stable isotope studies in enterally fed humans infants (n=7) using M+1 Phe and M+2 Arg, we found unexpectedly high levels of urinary enrichment, measured by tandem LC‐MS, of these amino acid isotopomers. Both isotopes had a D‐content of <0.2%. This led us to perform chiral LC column measurements to assess for D‐amino acid contamination. We found that on average 37% (range 30–50%) of total M+1 Phe was comprised of the D‐isoform. No D‐Phe was seen in plasma (n=4), and the enrichment of the L‐isoform was comparable in blood and urine. Similarly in urine (n=7) the D isoform of M+2 Arg comprised 82.5% (76–87), however, in plasma (n=4) the D‐content was significant comprising 22% (10–40%) of the total. We conclude that investigators using commercially produced, stable isotope labeled amino acids need to be aware that D‐contamination <0.2% may result in significant errors for enrichment, even in plasma, if chiral columns are not used. Supported by a grant from the CIHR.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 0.005 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".