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Infused and ingested labeled lysines: appearance in human-milk proteins
C S Irving1, E W Malphus, M R Thomas
1USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030.
The American Journal of Clinical Nutrition
|January 1, 1988
Summary
Stable isotope techniques successfully labeled human milk proteins using L-[13C1]lysine and L-[15N2]lysine. This method enables nutritional studies and investigation of milk protein synthesis kinetics in humans.
Area of Science:
- Nutritional Biochemistry
- Human Physiology
- Stable Isotope Tracing
Background:
- Investigating human milk protein synthesis requires reliable methods for labeling proteins.
- Stable isotope techniques offer a non-invasive approach to study metabolic processes in vivo.
Purpose of the Study:
- To determine if human milk proteins can be highly labeled using stable isotopes of lysine.
- To assess the feasibility of studying milk protein synthesis kinetics in lactating humans.
Main Methods:
- Administered intravenous L-[13C1]lysine and oral L-[15N2]lysine to fasted lactating subjects.
- Collected milk samples over 6 hours post-administration.
- Analyzed milk protein hydrolysates using gas chromatography-mass spectrometry isotope ratiometry.
Main Results:
- Significant labeling of milk protein was detected starting at 45 minutes post-administration.
- Peak labeling occurred at 150 minutes.
- Cumulative recovery of the tracer over 6 hours was 0.5%.
Conclusions:
- Human milk proteins can be effectively labeled using stable isotope techniques for nutritional studies.
- Stable isotope methods are suitable for investigating the in vivo kinetics of human milk protein synthesis.