Use of sulfate production as a measure of short-term sulfur amino acid catabolism in humans
Bibliographic record
Abstract
There is no fully satisfactory method for measuring amino acid catabolism in the nonsteady state that follows normal protein consumption. Because sulfate is the major product of sulfur amino acid catabolism, we tested whether its production can be accurately depicted using simple tracer or nontracer approaches under basal conditions and after the intravenous administration of a known amount of sulfate. In the basal postabsorptive state, serum sulfate concentration and urinary sulfate excretion remained constant for many hours, but the apparent steady-state serum sulfate rate of appearance achieved with primed continuous oral administration of sodium [(34)S]sulfate was 20% higher than urinary sulfate excretion. By contrast, after magnesium sulfate infusion, the increase in sulfate production above basal accounted for 95% over 6 h and 98% over 9 h of the administered dose when measured simply as urinary inorganic sulfate excretion corrected for changes in its extracellular fluid content. Using the latter method, we measured sulfate production after oral methionine and intravenous infusion of methionine in a mixture of other essential amino acids. Sulfate production above basal accounted for 59% over 6 h and 75% over 9 h of the oral methionine dose. Similar results were obtained with the mixed amino acid infusion, but interpretation of the latter experiment was limited by the mild protein sparing (and, hence, reduced endogenous sulfate production) induced by the amino acid infusion. We conclude that a simple nontracer method can provide an accurate measure of sulfate production and, hence, sulfur amino acid catabolism over collection periods as short as 6 h after a test meal. A significant portion of the sulfur derived from methionine appears to be retained in nonprotein compounds immediately after its ingestion.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| 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".