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Kex2-like proteolytic activity in adrenal medullary chromaffin granules
1Department of Biochemistry, Uniformed Services University of the Health Sciences, Bethesda, MD 20814.
Abstract:
This study demonstrates the presence of boc-Gln-Arg-Arg-MCA cleaving activity in bovine chromaffin granule membranes that resembles yeast Kex2 proteolytic activity. The chromaffin granule boc-Gln-Arg-Arg-MCA cleaving activity, like Kex2 proteolytic activity, shows calcium dependence, optimum activity at pH 7.5-8.2, inhibition by serine protease inhibitors, and preference for cleavage at the COOH-terminal side of Arg-Arg and Lys-Arg, over Lys-Lys, paired basic residues. Potent inhibition by the active-site directed inhibitor [D-Tyr]-Glu-Phe-Lys-Arg-CK (20 microM) provided further evidence for dibasic residue cleavage site specificity. These results are the first report of endogenous mammalian Kex2-like proteolytic activity that may be related to PC1/PC3 and PC2 enzymes, the newly discovered mammalian homologues of Kex2 protease. It will be important to determine the role of this Kex2-like proteolytic activity in processing the precursors of adrenal medullary neuropeptides.
Insights
Researchers found a Kex2-like enzyme in bovine chromaffin granules that cleaves specific protein sequences. This discovery sheds light on neuropeptide precursor processing in mammals.
Area of Science:
- Biochemistry
- Molecular Biology
- Neuroscience
Background:
- Bovine chromaffin granule membranes possess proteolytic activities crucial for neuropeptide processing.
- Yeast Kex2 protease is a well-characterized enzyme involved in protein maturation.
Purpose of the Study:
- To characterize the boc-Gln-Arg-Arg-MCA cleaving activity in bovine chromaffin granule membranes.
- To determine if this activity resembles yeast Kex2 proteolytic activity.
- To investigate the potential role of this activity in mammalian neuropeptide precursor processing.
Main Methods:
- Enzyme activity assays using the substrate boc-Gln-Arg-Arg-MCA.
- Characterization of enzyme properties including calcium dependence, pH optimum, and inhibition by protease inhibitors.
- Testing the specificity of cleavage at dibasic residue sites.
- Inhibition studies using a specific active-site directed inhibitor.
Main Results:
- Bovine chromaffin granule membranes exhibit boc-Gln-Arg-Arg-MCA cleaving activity.
- This activity is calcium-dependent, with an optimal pH of 7.5-8.2.
- The enzyme is inhibited by serine protease inhibitors and shows specificity for cleaving at Arg-Arg and Lys-Arg sites.
- An active-site directed inhibitor ([D-Tyr]-Glu-Phe-Lys-Arg-CK) potently inhibited the activity.
Conclusions:
- The study identifies an endogenous mammalian Kex2-like proteolytic activity in bovine chromaffin granules.
- This activity shares functional similarities with yeast Kex2 protease.
- The findings suggest a potential link to mammalian prohormone convertases PC1/PC3 and PC2.
- Further research is needed to elucidate the role of this enzyme in processing adrenal neuropeptide precursors.