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Yeast inorganic pyrophosphatase substrate recognition
Archives of Biochemistry and Biophysics
|November 1, 1983
Summary
Yeast inorganic pyrophosphatase acts on bidentate pyrophosphate complexes, with activity influenced by metal-ligand composition. Metal-water ligands play a role in productive binding and hydrolysis rates, with varying effects under Mg2+ and Zn2+ activation.
Area of Science:
- Biochemistry
- Enzymology
- Inorganic Chemistry
Background:
- Inorganic pyrophosphatase (IPPase) is a crucial enzyme in cellular metabolism, catalyzing pyrophosphate hydrolysis.
- The substrate specificity and catalytic mechanisms of IPPases are influenced by the structure and coordination of pyrophosphate complexes.
Purpose of the Study:
- To investigate the substrate activity of various metal-dipyrophosphate complexes with yeast inorganic pyrophosphatase.
- To elucidate the role of metal-ligand composition, particularly metal-aqua ligands, in enzyme binding and catalysis.
- To compare the activity of Mg2+-activated and Zn2+-activated enzyme towards different pyrophosphate complexes.
Main Methods:
- Synthesis and characterization of various metal-dipyrophosphate complexes, including cobalt and chromium complexes with varying ligands.
- Enzymatic assays using yeast inorganic pyrophosphatase to determine kinetic parameters (Km, kcat) for substrate hydrolysis.
- Investigation of enzyme activity under different metal ion activations (Mg2+ and Zn2+).
Main Results:
- Monodentate Co(NH3)5PPi is not a substrate, while P1,P2-bidentate Co(NH3)4PPi is hydrolyzed at 7.5 min-1.
- For P1,P2-bidentate Cr-PPi complexes, increasing ammonia substitution for water ligands decreased binding affinity and turnover number.
- Mg2+-activated enzyme did not hydrolyze beta, gamma-bidentate or alpha, beta, gamma-tridentate Co-PPPi complexes, but Zn2+-activated enzyme hydrolyzed the tridentate complex at 0.17 min-1.
Conclusions:
- Yeast inorganic pyrophosphatase exhibits specificity towards bidentate pyrophosphate complexes, with activity modulated by metal coordination.
- Metal-aqua ligands influence substrate binding and catalytic efficiency, with ammonia substitution reducing activity.
- The enzyme's metal ion cofactor (Mg2+ vs. Zn2+) significantly impacts its substrate specificity and hydrolysis capability for different pyrophosphate coordination modes.