Photosynthetica X:X | DOI: 10.32615/ps.2026.004

Elucidating copper ion interactions with carbonic anhydrase: insights from fluorescence quenching and thermodynamic analysis

M.S. SHABANOVA1, I.M. HUSEYNOVA1, S.K. ZHARMUKHAMEDOV2, S.I. ALLAKHVERDIEV2, 3, 4, 5
Institute of Molecular Biology, Ministry of Science and Education of the Republic of Azerbaijan, 11 Izzat Nabiyev Str., AZ1073, Baku, Azerbaijan1
2 Institute of Basic Biological Problems, Russian Academy of Sciences, Institutskaya Street 2, 142290 Pushchino, Moscow Region, Russia
3 Department of Plant Physiology, Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119991 Moscow, Russia
4 K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, 127276 Moscow, Russia
5 Faculty of Engineering and Natural Sciences, Bahcesehir University, Istanbul, Turkey

Plant carbonic anhydrases (CAs) are essential metalloenzymes catalyzing reversible hydration of CO2 to HCO3⁻, thereby optimizing photosynthetic efficiency and carbon fixation in plants. They facilitate CO2 delivery to Rubisco, enhance carbon assimilation, and play a role in plant responses to stresses (such as drought, high salinity) by modulating stomatal conductance and internal CO2 concentrations. Despite the well-established physiological importance of plant CAs, the influence of metal ions, particularly copper (Cu2+), on their structure and activity remains inadequately understood. Here, bCA II is used as a well-characterized model enzyme to investigate enzyme-metal interactions. We employed intrinsic tryptophan and tyrosine fluorescence quenching to elucidate the binding mechanism of Cu2+ with bCA II. Our results demonstrate static quenching, indicative of ground-state complex formation, with binding parameters assessed at 288 K and 298 K [Kb = (2.64 ± 0.15 and 1.68 ± 0.54) × 103, M-1, n ≈ 1] and negative ΔG°, ΔH°, ΔS°.

Additional key words: bovine CA II; copper ions; enzyme-metal interaction; fluorescence quenching; plant carbonic anhydrase; thermodynamics.

Received: February 12, 2026; Revised: February 27, 2026; Accepted: March 2, 2026; Prepublished online: March 10, 2026 

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