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Stabilisation of cathepsin E by ATP
D J Thomas1, A D Richards, R A Jupp
1Department of Biochemistry, University College, Cardiff, Wales.
Insights
Adenosine triphosphate (ATP) restores activity to human cathepsin E at pH 5.8, demonstrating its crucial role in enzyme function. This finding highlights ATP
Area of Science:
- Biochemistry
- Enzymology
- Human Physiology
Background:
- Cathepsin E is a key aspartic protease found in human red blood cells and gastric mucosa.
- Its enzymatic activity is pH-dependent and its regulation in physiological conditions remains incompletely understood.
Purpose of the Study:
- To investigate the effect of adenosine triphosphate (ATP) on the hydrolytic activity of human cathepsin E.
- To determine the pH-dependent modulation of cathepsin E by ATP and its analogues.
Main Methods:
- Assessed the hydrolysis rates of three distinct substrates using purified human cathepsin E.
- Measured enzyme activity across a range of pH values in the presence and absence of ATP.
- Utilized a non-hydrolyzable methylene-ATP analogue to probe the mechanism of activation.
Main Results:
- ATP had no significant effect on cathepsin E activity below pH 5.0.
- At pH 5.8, ATP and a methylene-ATP analogue restored virtually inactive cathepsin E to full catalytic efficiency (kcat).
- Enzyme activity progressively decreased at higher pH values, yet remained detectable at pH 7.0.
Conclusions:
- Adenosine triphosphate (ATP) plays a critical role in modulating human cathepsin E activity, particularly at near-neutral pH.
- The activation mechanism involves ATP binding, independent of its hydrolysis.
- These findings suggest a novel regulatory pathway for cathepsin E in human physiological environments.
Abstract:
The hydrolysis of 3 distinct substrates by cathepsin E from human red blood cells and gastric mucosa was measured in the presence and absence of physiologically relevant concentrations of ATP. At pH values below about 5.0, the nucleotide was without effect. However, at pH 5.8, whereas cathepsin E was virtually inactive by itself, it was restored to full activity (kcat) by ATP and the non-hydrolysable methylene-ATP analogue. At still higher pH values, kcat progressively diminished but significant levels of cathepsin E activity were readily detectable at pH 7.0. The specificity of this stabilisation effect was examined.