The pH-dependence of pepsin-catalysed reactions.

Area of Science:

• Biochemistry
• Enzymology
• Protein Chemistry

Background:

• Pepsin is a key digestive enzyme.
• Understanding pepsin's pH-dependent activity is crucial for its function.
• Previous studies have explored enzyme kinetics and pH effects.

Purpose of the Study:

• To investigate the pH-dependence of pepsin-catalyzed hydrolysis.
• To determine the apparent pK(a) values for pepsin and its substrates.
• To elucidate the role of enzyme ionization in catalytic activity.

Main Methods:

• Continuous monitoring of ninhydrin-positive product formation.
• Kinetic analysis of peptide hydrolysis across a pH range.
• Determination of rate constants (k(0)) and Michaelis constants (K(m)).

Main Results:

• Pepsin hydrolysis rates are influenced by the ionization of two groups with apparent pK(a) values of 1.0 and 4.7.
• Acidic peptide substrates showed different apparent pK(a) values (1.1 and 3.5) compared to a neutral substrate (1.0 and 4.7).
• Anions of acidic substrates exhibit minimal binding to the pepsin enzyme.

Conclusions:

• Pepsin's catalytic rate is regulated by the ionization state of specific enzyme groups.
• The observed kinetics reflect the interplay between enzyme ionization and substrate binding.
• Pepsin enzyme kinetics are sensitive to both pH and substrate chemical properties.