Inhibition of Escherichia coli Inorganic Pyrophosphatase by Fructose-1-phosphate

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Pyrophosphate (PPi) is crucial for cellular energy metabolism and biosynthesis.
• Inorganic pyrophosphatase (PPase) controls intracellular PPi levels in E. coli.
• Mechanisms regulating PPase activity remain incompletely understood.

Purpose of the Study:

• To elucidate the regulatory mechanisms of inorganic pyrophosphatase activity.
• To investigate the inhibitory effect of fructose-1-phosphate (Fru-1-P) on PPase.
• To determine the binding site and mode of inhibition for Fru-1-P.

Main Methods:

• Enzyme kinetics assays to determine inhibition constants.
• Site-directed mutagenesis of specific amino acid residues in the regulatory site.
• Analysis of Fru-1-P inhibition in wild-type and mutant PPase enzymes.

Main Results:

• Fru-1-P inhibits PPase activity through non-competitive inhibition with respect to the substrate.
• The inhibition constant (Ki) for Fru-1-P binding to the enzyme-substrate complex is 1.1 mM.
• Mutations in key residues (Lys112, Lys115, Lys148, Arg43) within the regulatory site abolished or reduced Fru-1-P inhibition.

Conclusions:

• Fru-1-P acts as a physiological inhibitor of E. coli inorganic pyrophosphatase.
• Inhibition occurs via a specific regulatory site, distinct from the enzyme's active site.
• Specific amino acid residues are critical for mediating Fru-1-P-induced regulation of PPase activity.