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Enkephalin hydrolysis by human serum biotinidase
1National Children's Medical Research Center, Tokyo, Japan.
Biochimica Et Biophysica Acta
|August 6, 1991
Summary
Human serum biotinidase acts as an aminopeptidase, efficiently hydrolyzing opioid-neuropeptides like enkephalins. This enzyme also cleaves biocytin, suggesting a dual role in both vitamin metabolism and neuropeptide regulation.
Area of Science:
- Biochemistry
- Enzymology
Background:
- Human serum biotinidase is primarily known for its role in biotin metabolism.
- Its broader enzymatic activities and physiological relevance remain under investigation.
Purpose of the Study:
- To investigate the peptidase activity of purified human serum biotinidase.
- To identify optimal peptide substrates and characterize the enzyme's catalytic mechanism.
Main Methods:
- Enzyme kinetics (kcat/Km) were measured using various physiological peptides and biocytin.
- Inhibition studies were performed using antibiotics, metal ions, and chelating agents.
Main Results:
- Human serum biotinidase demonstrated significant amino-exo-peptidase activity, with enkephalins and dynorphin A as preferred substrates.
- The enzyme exhibited similar catalytic efficiency (kcat/Km) for neuropeptides and biocytin.
- Hydrolysis was dependent on a free amino group at the C-terminus and involved a Zn-dependent catalytic center.
- Biocytin uniquely inhibited the enzyme's aminopeptidase activity.
Conclusions:
- Human serum biotinidase possesses a dual function, acting as both a biocytin amidase and a neuropeptide-degrading aminopeptidase.
- This dual activity may explain its high concentration in serum and its potential role in regulating neuropeptide levels.