Effects of functional group-specific complexation and adsorption of phytic acid on its degradation by phytase

As one of the most predominant organic phosphorus (P) species in many soils, phytic acid could serve as a potentially important mineralizable P reservoir in soils and sediments. However, the active interaction between phytic acid and metals or minerals has rendered phytic acid recalcitrant against mineralization. The mechanisms of phytic acid adsorption on the calcite-water interface haven’t been clearly investigated. Furthermore, how phytic acid-Ca2+, or phytic acid-calcite interaction affects the activity of phytase, a group of enzymes that can mineralize phytic acid, remains unclear. This study, therefore, investigated the adsorption mechanism of phytic acid at the calcite-water interface, and how Ca2+ (aq) or calcite affected phytase activity using different spectroscopic techniques. Phytic acid was predominantly adsorbed via outer-sphere complexation at pH 6 and pH 8, which was supported by: i) a lack of significant change in the zeta potential of phytic acid reacted-calcite; and ii) a fast exchange between free phytic acid and adsorbed phytic acid. The results also showed functional group specificity of phytic acid and phytic acid structural change during the adsorption. Batch degradation kinetic experiments showed that phytase activity followed Michaelis-Menten kinetics at pH 6, and the increased Km and decreased Vmax with Ca2+/calcite addition indicated a mixed inhibition mechanism, which was likely due to the allosteric effects of Ca2+/calcite, which altered the phytase secondary structure. The phytase used in this study was also observed to target the phosphate at the D/L-3 position on a phytic acid molecule at pH 6. The overall phytase activity decreased at pH 8 due to the denaturing effect of the alkaline pH, while Ca2+/calcite addition enhanced phytase activity, which was attributed to the structural change of phytic acid upon complexation. Additionally, in the case of calcite, the stabilization of phytase conformation when interacting with the mineral interface also contributed to enhanced activity. Contrary to what was observed at pH 6, the target of phytase was P5 at pH 8. Consequently, the solubility, mineralization, and bioavailability of phytic acid in soils rich in calcite largely depend on the mutual interaction among phytic acid, phytase, and Ca2+ (aq)/calcite, which is affected by soil conditions (e.g., pH, solution composition).

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Chen, Ai

Contributors dc:contributor

• Arai, Yuji
• Mulvaney, Richard
• Han, Hee-Sun
• Zhu, Lingyang

• Phosphorus
• Mineralization
• Nmr
• Calcite
• Phytase

Statement dc:rights

• Copyright 2023 Ai Chen

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/121222

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F121222