Normalized Labeling

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Found in the PeakGroups data format.

Normalized labeling is the enrichment in a compound normalized to the enrichment among the tracer compound(s) from the final serum timepoint from the same animal.

normalized_labeling = enrichment_fraction / serum_tracers_enrichment_fraction

See:

Example

Normalized labeling in alanine (C3H7NO2) and glutamate (C5H9NO4) measured in the final serum sample and one tissue (quadricep) sample from an infusion of [13C3-15N]-alanine:

Tissue Measured
Compound(s)		 Labeled
Element		 Total
Abundance		 Enrichment
Fraction		 Enrichment
Abundance		 Normalized
Labeling
serum_plasma_tail alanine C 1721209 0.275916 474909.5 1
serum_plasma_tail alanine N 1721209 0.344919 593677.6 1
serum_plasma_tail glutamate C 242215.7 0.018 4359.787 0.065236
serum_plasma_tail glutamate N 242215.7 0.053935 13063.83 0.156369
quadricep alanine C 97694902 0.006183 604078.4 0.02241
quadricep alanine N 97694902 0.019993 1953218 0.057964
quadricep glutamate C 14251992 0.007268 103580.9 0.026341
quadricep glutamate N 14251992 0.087257 1243586 0.252978

In some cases, a labeled element present in a tracer is not found in a measured compound, and Normalized Labeling is not reported. For example, lactate (C3H6O3) can be measured in samples from an animal infused with N-labeled glutamine (C5H10N2O3), but no nitrogen enrichment or normalized labeling is reported for lactate.

For infusates with multiple tracers, the serum tracers enrichment fraction is the average of enrichment in each serum tracer group.

The selection of the serum tracer peak groups to use, when multiple instances have been picked, depends on the following:

  • If multiple serum samples were collected on the same date and same minutes after the start of infusion, (i.e. they are biological replicates), the specific tracer peak group selected for each tracer is arbitrary.
  • If a serum tracer peak group is present in multiple MSruns (appears in multiple AccuCor files), the most recently uploaded data is selected.

Serum Tracers Enrichment Fraction

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Normalized labeling relies on the calculation of a weighted average of the enrichment fraction of labeled atoms among of all of the infused tracers in the animal's final serum sample. E.g. The fraction of labeled carbons among all the final serum sample's tracer compounds.

This calculation is performed for a single labeled element in the following manner:

The label enrichment is summed for all of the tracers in the last serum sample, and is divided by the total count of the element among all the tracers' formulas (labeled or not).

serum_tracers_enrichment_fraction = ∑_tracer_peak(fraction * labeled_count) / element_count

Where:

  • ∑_tracer_peak stands for the sum across all tracer peaks/observations.
  • labeled_count refers to the number of labeled elements in a single tracer observation (/peak).
  • element_count is the number of occurrences the element summed across all tracers' formulas (labeled or not).
  • fraction: See Fraction