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Tonin-like activity present in the human submandibular gland
M P Gualberto1, R L Nunes, W T Beraldo
1Department of Physiology and Biophysics, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Agents and Actions. Supplements
|January 1, 1992
Summary
Researchers purified a novel enzyme from the human submandibular gland that generates angiotensin II. This enzyme exhibits distinct pH optima and significantly lower activity compared to its rat counterpart.
Area of Science:
- Biochemistry
- Enzymology
- Human Physiology
Background:
- The renin-angiotensin system (RAS) plays a crucial role in regulating blood pressure and fluid balance.
- Angiotensin II is a key effector peptide within the RAS.
- The presence and characterization of angiotensin II-generating enzymes in human tissues are of significant physiological interest.
Purpose of the Study:
- To purify and characterize an enzyme responsible for liberating angiotensin II from its precursors in the human submandibular gland.
- To determine the enzyme's molecular weight, sensitivity to inhibitors, and optimal pH for activity.
- To compare the angiotensin II-generating activity in the human submandibular gland with that of the rat gland.
Main Methods:
- Purification of the enzyme from human submandibular gland extract.
- Determination of molecular weight using standard biochemical techniques.
- Enzyme inhibition assays using phenylmethylsulfonyl fluoride (PMSF), EDTA, and enalaprilat.
- Assessing enzyme activity at various pH levels with different angiotensin substrates.
Main Results:
- An enzyme capable of liberating angiotensin II was successfully purified.
- The enzyme has a molecular weight of 110,000 Da and is inhibited by PMSF but not by EDTA or enalaprilat.
- Optimal pH for angiotensin II liberation varied: 4.0 for angiotensin I, 7.0 for angiotensinogen(1-14) fragment, and 8.0 for angiotensinogen.
- Human submandibular gland exhibits 5,000-fold less angiotensin II generating activity than the rat gland.
Conclusions:
- A novel angiotensin II-generating enzyme exists in the human submandibular gland.
- The enzyme's properties suggest it is a distinct entity with specific substrate preferences and pH optima.
- The significantly lower activity in humans compared to rats indicates potential species-specific differences in local angiotensin II regulation within this gland.