Enzymes of phosphorus cycling: releasing orthophosphate Which enzymes catalyze the liberation of orthophosphate (Pi) from organic phosphorus compounds and from inorganic pyrophosphate in biological systems?

Introduction / Context:
Phosphorus turnover in cells and ecosystems depends on enzymes that release inorganic phosphate from organic substrates. These activities are crucial in nutrient cycling, biotechnology assays, and diagnostic tests. Recognizing the correct enzyme class helps interpret lab results and environmental processes.

Given Data / Assumptions:

• Target reaction: hydrolytic cleavage to liberate orthophosphate (Pi).
• Substrates include organic phosphate esters and inorganic pyrophosphate (PPi).
• Physiological pH may vary; alkaline variants are widely used/measured.

Concept / Approach:

Phosphatases hydrolyze phosphate esters to release Pi. Alkaline phosphatases are active at alkaline pH and can also act on pyrophosphate (with specific pyrophosphatases also contributing). In contrast, oxidoreductases change oxidation states; proteases hydrolyze peptide bonds; hydrogenases interconvert protons and hydrogen gas.

Step-by-Step Solution:

Verification / Alternative check:

Clinical chemistry assays for serum alkaline phosphatase activity use chromogenic phosphate esters, monitoring Pi release; microbial extracellular phosphatases mobilize phosphorus from organic matter.

Why Other Options Are Wrong:

• Oxidoreductase/Dehydrogenase: Catalyze redox, not phosphate ester hydrolysis.
• Protease: Targets peptide bonds, not phosphate esters.
• Hydrogenase: Involves H2/H+ interconversion, unrelated to Pi release.

Common Pitfalls:

• Confusing pyrophosphatase specificity with general phosphatase action; many alkaline phosphatases have PPi activity.

Final Answer:

Alkaline phosphatases