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A cryptic meprin-like proteolytic activity in mouse kidney brush border membranes
G C Macadam1, R J Beynon, J S Bond
1Department of Biochemistry, University of Liverpool, England.
Abstract:
1. Inbred mouse strains differ markedly in the expression of a kidney brush border metalloendopeptidase, meprin-a. 2. Brush border preparations from mice of the low-meprin-a phenotype (specific activities less than 5% of the high-meprin-a trait) contain a metallo-endopeptidase, meprin-b, that is larger than meprin-a, and which is inactive unless the membrane preparations are treated with trypsin. 3. This cryptic metallo-endopeptidase has been previously postulated to be a stalled precursor of meprin-a. 4. We show here that meprin-b is present in all mice-high and low meprin-a phenotypes--and that this activity is similar in substrate specificity and amount present in the brush border. 5. Meprin-b may therefore be a distinct gene product that is independent of meprin-a phenotype.
Insights
Mice possess a kidney enzyme, meprin-b, regardless of meprin-a levels. This inactive enzyme, meprin-b, is present in all mice and may be a separate gene product, not a precursor.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Inbred mouse strains exhibit significant variations in the expression of the kidney brush border enzyme meprin-a.
- Low meprin-a phenotype mice have a distinct metalloendopeptidase, meprin-b, in brush border preparations.
Purpose of the Study:
- To investigate the presence and nature of meprin-b in different mouse phenotypes.
- To determine if meprin-b is a precursor to meprin-a or an independent gene product.
Main Methods:
- Analysis of kidney brush border preparations from mice with high and low meprin-a phenotypes.
- Enzyme activity assays and characterization of meprin-b.
- Trypsin treatment to activate cryptic metalloendopeptidase activity.
Main Results:
- Meprin-b was detected in all tested mice, irrespective of their meprin-a phenotype.
- Meprin-b activity showed similar substrate specificity and abundance in both high and low meprin-a groups.
- Meprin-b is a larger, trypsin-activated metalloendopeptidase distinct from meprin-a.
Conclusions:
- Meprin-b is present in all mice and is not solely associated with the low meprin-a phenotype.
- The characteristics of meprin-b suggest it is a distinct gene product, independent of meprin-a.
- Meprin-b is not a stalled precursor of meprin-a but rather a separate entity.