Apparent kinetic properties of soil phosphomonoesterase and β‐glucosidase are disparately influenced by pH. Issue 6 (2nd November 2021)

• Record Type: Journal Article
• Authors: Li, Chongyang; Margenot, Andrew J.
• Is Part Of: Soil Science Society of America Journal. Volume 85:Issue 6(2021)
• Page Start: 2007
• Page End: 2018
• Publication Date: 2021-11-02
• Subjects: Soils -- United States -- Periodicals; Soil science -- Periodicals; Periodicals; 631.4973
• DOI: 10.1002/saj2.20332
• Languages: English
• ISSNs: 0361-5995

Abstract

Abstract: Extracellular enzymes catalyze organic matter transformations in soils, yet the study of soil enzymes does not typically evaluate how enzyme kinetic properties that govern activity in situ may shift with environmental parameters such as pH. To test this, we quantified changes in apparent kinetic properties (maximum catalysis rate [ App V max ] and substrate concentration that produces 50% of V max [ App K m ]) of soil phosphomonoesterase (PME) and β‐glucosidase (BG) as a function of pH by using dual gradients of buffer pH (3–12) and substrate concentrations in a selected set of diverse soils. A third kinetic property, apparent specificity constant ( App K a = App V max / App K m ) was also evaluated as a function of pH. Results indicated widely differing pH optima of soil PME and BG App V max and App K m, decoupling of which entailed unpredictable pH optima of App K a . Additionally, changes in soil enzyme activity with pH may not be driven by shifts in the specificity constant because pH– App V max relationships are largely unrelated to co‐occurring changes in App K a . These results invalidate the assumption that K m of a soil enzyme is constant across pH and emphasize the importance of assaying soil enzyme activities at sufficiently high (5 × K m ) substrate concentrations at a given pH to avoid the mischaracterizing pH optima. Core Ideas: Soil enzyme kinetic properties ( V max, K m, K a ) may be sensitive to pH. Enzyme V max and K m showed strong soil‐ and enzyme‐specific sensitivity to pH. Decoupling of enzyme V max and K m means that K a is not predictable. Enzymological principle of K m sensitivity to pH appears to hold true for soil enzymes.