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A low-molecular-weight inhibitor of the neutral proteinase from rat intestinal smooth muscle
Abstract:
1. Rat intestinal smooth muscle was shown to contain endogenous inhibitory activity towards the neutral trypsin-like muscle proteinase described previously [Beynon & Kay (1978) Biochem. J. 173, 291--298]. 2. Comtamination of the muscle tissue by mucosal, blood and pancreatic inhibitors was shown to be unlikely. 3. The inhibitory activity was resolved into high- and low-molecular-weight components. 4. The low-molecular-weight component was purified to homogeneity. It has a molecular weight of approx. 9000 and was stable over the pH range 3--11. 5. It inhibited the muscle proteinase competitively (Ki congruent to t microM), but had no effect on any of the other proteinases tested. 6. Leupeptin also inhibited the muscle proteinase competitively (Ki congruent to 0.3 microM), whereas the low-molecular weight proteins gastrin, glucagon and insulin B-chain had very little effect. 7. A role for a weakly binding inhibitor in modulating the influence of the neutral proteinase on intracellular protein degradation is considered.
Insights
Researchers identified a novel low-molecular-weight inhibitor in rat intestinal smooth muscle. This inhibitor specifically targets a neutral trypsin-like muscle proteinase, suggesting a role in regulating intracellular protein degradation.
Area of Science:
- Biochemistry
- Molecular Biology
- Physiology
Background:
- Rat intestinal smooth muscle contains endogenous inhibitory activity.
- This activity is directed against a previously described neutral trypsin-like muscle proteinase.
- Contamination by other inhibitors is unlikely.
Purpose of the Study:
- To characterize the endogenous inhibitory activity in rat intestinal smooth muscle.
- To isolate and purify the low-molecular-weight inhibitory component.
- To investigate the inhibitory mechanism and specificity.
Main Methods:
- Resolution of inhibitory activity into high- and low-molecular-weight components.
- Purification of the low-molecular-weight component to homogeneity.
- Enzyme inhibition assays to determine specificity and mechanism (competitive inhibition).
Main Results:
- A homogeneous low-molecular-weight inhibitor (approx. 9000 Da) was isolated, stable across a wide pH range (3-11).
- The inhibitor competitively inhibited the target muscle proteinase (Ki ≈ 1 µM) but not other tested proteinases.
- Leupeptin also competitively inhibited the muscle proteinase (Ki ≈ 0.3 µM), while other small proteins had minimal effect.
Conclusions:
- A specific, low-molecular-weight inhibitor of the rat intestinal muscle proteinase exists.
- This inhibitor is distinct from common proteinase inhibitors and small peptides.
- It may play a role in modulating intracellular protein degradation by the muscle proteinase.