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Synthesis of alpha 1-microglobulin by guinea-pig liver
Abstract:
Explants from perfused guinea-pig livers were found to release alpha 1-microglobulin into the culture medium. Tritiated leucine in the medium was incorporated into the protein, suggesting a de novo synthesis of alpha 1-microglobulin by the liver tissue. The size of the protein could not be distinguished from that of purified urinary alpha 1-microglobulin when tested with sodium dodecyl sulfate/polyacrylamide gel electrophoresis. After intravenous injections of tritiated leucine into guinea-pigs, the 105 000 X g pellet of homogenized liver rapidly increased its content of radioactive alpha 1-microglobulin, with a maximum after 20 min. 3H-Labelled alpha 1-microglobulin appeared in serum after a lag phase of 20 min, and by comparing the rate of accumulation with albumin, the synthesis of guinea-pig alpha 1-microglobulin could be estimated to 20 micrograms g liver-1 h-1.
Insights
Guinea-pig livers synthesize alpha 1-microglobulin (A1M), a protein found in urine. This study confirms de novo synthesis by liver tissue using radiolabeled leucine, estimating production rates.
Area of Science:
- Biochemistry
- Cell Biology
- Proteomics
Background:
- Alpha 1-microglobulin (A1M) is a low molecular weight protein found in various biological fluids, including urine.
- The tissue of origin and synthesis rate of A1M in guinea-pigs were previously unclear.
Purpose of the Study:
- To investigate the synthesis of alpha 1-microglobulin (A1M) in guinea-pig liver tissue.
- To determine if liver explants and in vivo administration of radiolabeled precursors confirm de novo A1M synthesis.
Main Methods:
- Perfusion of guinea-pig liver explants with tritiated leucine to assess protein synthesis.
- Sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) to analyze protein size.
- Intravenous injection of tritiated leucine into guinea-pigs followed by liver and serum analysis.
Main Results:
- Liver explants released alpha 1-microglobulin (A1M) that incorporated tritiated leucine, indicating de novo synthesis.
- SDS-PAGE confirmed the synthesized A1M size matched purified urinary A1M.
- In vivo, radioactive A1M accumulated rapidly in liver tissue and appeared in serum, with estimated synthesis at 20 micrograms/g liver/hour.
Conclusions:
- The liver is a primary site for the de novo synthesis of alpha 1-microglobulin (A1M) in guinea-pigs.
- The synthesized A1M is biochemically similar to urinary A1M.
- Quantification of A1M synthesis provides a baseline for further physiological and pathological studies.