---
title: "Metabolic Flux & Isotope Tracing Guide"
lang: en
url: https://www.gereallife.com/en/services/resources-flux-guide.html
canonical: https://www.gereallife.com/en/services/resources-flux-guide.html
entity: Shanghai Gereallife Biotech Co., Ltd
updated: 2026-11-02
---
KEY POINTS 
 
- Concentration is not flux: static metabolomics sees pool size, tracing sees turnover
- The tracer defines the conclusion: 13C-glucose for glycolysis/TCA, 13C-glutamine for anaplerosis, 15N for amino-acid turnover
- Time-series sampling is mandatory: a single end point cannot be fitted
- Isotope corrections are essential: natural abundance, tracer purity and fragment corrections 
 
 
 

## 011. When flux analysis is required

 
- Metabolite levels are unchanged after treatment, but the phenotype (proliferation, differentiation, secretion) clearly shifts
- You need to separate increased synthesis from decreased degradation — static data cannot
- You want to prove that an enzyme or transporter change actually alters pathway flux
- Flux-driven fields: tumour metabolic reprogramming, immune cell activation, fermentation process optimisation 

If the question is simply "which metabolites differ between groups", untargeted metabolomics is enough — tracing adds cost and complexity.

 
 
 

## 022. Design essentials

 

| Element | Recommendation | Common mistake |
| --- | --- | --- |
| Tracer | 13C6-glucose (glycolysis/TCA), 13C5-glutamine (anaplerosis), 13C3-lactate, 15N-amino acids | Unlabelled tracer or unknown isotopic purity |
| Labelling time | At least 4–6 time points (e.g. 0/15/30/60/120/240 min) | A single end point |
| Medium design | Tracer replaces the corresponding unlabelled nutrient, everything else identical | Different tracer concentration from routine culture, distorting flux |
| Quenching and extraction | Fast quench (cold methanol / liquid nitrogen) to stop turnover | Prolonged room-temperature centrifugation |
| Replicates | At least 4–6 per group, including the 0 time point | No zero point, so natural abundance cannot be subtracted |

 
 
 
 

## 033. From isotope patterns to flux

 

Once the isotopologue distribution (M+0, M+1 … M+n) is measured, there are two routes:

 
- Isotopically steady state: label to plateau, then infer flux ratios from the M+ distribution. Simpler and robust — suitable for most biological questions.
- Non-stationary INST-MFA: fit the time-series curves to obtain absolute fluxes (nmol per 10⁶ cells per hour); requires more time points and stricter model assumptions. 

A proper report states the raw isotopologue data, the correction method, the flux model and confidence intervals. Descriptions such as "the M+3 fraction increased" are not flux analysis.

 
 
 

## 044. Five questions to ask a provider

 
- Do you measure isotopologue distributions only, or also compute flux? The workload differs by an order of magnitude.
- How are natural abundance and tracer purity corrected, and is MS2 fragment correction applied?
- Who designs the time points? If I can only provide an end-point sample, can flux still be reported?
- Which model or software is used (influx_s, 13CFLUX2, an in-house INST-MFA pipeline)?
- Can you measure labelled metabolites both intracellularly and in the medium? 
 
 
 

## 055. Gereallife flux services

 

Gereallife (Shanghai Gereallife Biotech Co., Ltd.) provides 13C/15N isotope tracing and metabolic flux analysis: tracer experiment design, time-series sampling, LC-MS isotopologue measurement, natural-abundance correction and flux estimation. Projects are often combined with untargeted or targeted metabolomics so that static differences and flux conclusions corroborate each other.

 
 
 

## Q&AFAQ

 Is 13C always required? Mostly yes. 15N is used for amino-acid and nucleotide turnover and 2H for specific pathways such as gluconeogenesis, but flux modelling is most mature with 13C. 
 Can flux be calculated from an end point only? Full INST-MFA is not possible. If labelling has reached steady state, flux ratios can be estimated, but the conclusions are coarser and must be agreed in advance. 
 Should flux and metabolomics be combined? Yes — run static metabolomics on the same samples first to find differences, then use tracing to determine whether they arise from flux or pool-size changes. 
 
 
 
 
 
 Need study design? 
 

Free study design and sample assessment, response within 1 hour.

 Contact the team → 
 
 
 
 

 
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