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Biosynthesis and degradation of meprins, kidney brush border proteinases
J L Hall1, E E Sterchi, J S Bond
1Department of Biochemistry and Molecular Biophysics, Virginia Commonwealth University, Richmond 23298-0614.
Abstract:
Meprins, which are cell surface metalloendopeptidases, consist of two types of subunits, alpha and beta. Genetic factors determine which subunits and oligomeric forms of the enzyme exist in kidney in different strains of mice. In order to further explore factors that determine the concentration and activity of meprins, the rates of biosynthesis and degradation of the meprin subunits were determined in an organ culture system using ICR and C3H/He mouse kidneys. In biosynthesis experiments, the rate of incorporation of radiolabeled amino acids into immunoprecipitable forms of the alpha and beta subunits was determined. The rate of loss of radiolabel from the subunits was measured in pulse-chase experiments to determine the half-lives of the subunits. The rate of synthesis of the alpha subunit was twofold greater than that of the beta subunit: 861 +/- 32 vs 361 +/- 23 dpm/micrograms subunit protein/min for alpha vs beta. The rate of synthesis for total kidney protein in both strains was approximately 700 dpm/micrograms/min. The half-life for alpha was 8.9 +/- 0.24 h compared to 12.1 +/- 0.7 h for beta; the half-life for total protein in kidney was approximately 35 h. Thus, the half-lives of alpha and beta were similar and shorter than the half-lives of the average protein in kidney cells. The higher rate of synthesis of alpha is probably responsible for the greater abundance of this protein compared to beta in microvillus membranes.
Insights
The alpha subunit of meprin metalloendopeptidases is synthesized at twice the rate of the beta subunit. This higher synthesis rate explains the greater abundance of the alpha subunit in kidney microvillus membranes.
Area of Science:
- Biochemistry
- Molecular Biology
- Proteomics
Background:
- Meprins are cell surface metalloendopeptidases composed of alpha and beta subunits.
- Genetic factors influence meprin subunit composition and oligomeric forms in mouse kidneys.
- Understanding meprin subunit biosynthesis and degradation is crucial for elucidating enzyme concentration and activity.
Purpose of the Study:
- To investigate the rates of biosynthesis and degradation of meprin alpha and beta subunits.
- To determine the factors influencing meprin subunit concentration and activity in mouse kidneys.
Main Methods:
- Organ culture system using ICR and C3H/He mouse kidneys.
- Biosynthesis experiments measuring radiolabeled amino acid incorporation into meprin subunits.
- Pulse-chase experiments to determine the half-lives of meprin subunits.
Main Results:
- The alpha subunit exhibited a synthesis rate twofold greater than the beta subunit (861 vs 361 dpm/micrograms/min).
- Half-lives of alpha (8.9 h) and beta (12.1 h) subunits were similar and shorter than total kidney protein (approx. 35 h).
- Higher alpha subunit synthesis rate correlates with its greater abundance in microvillus membranes.
Conclusions:
- Differential synthesis rates, not degradation rates, primarily determine the relative abundance of meprin alpha and beta subunits.
- The alpha subunit's higher synthesis rate accounts for its predominant presence in kidney microvillus membranes.
- These findings provide insights into the regulation of meprin enzyme composition and function.