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Kinetics and thermodynamics for aldo/keto conversion of D‐xylose and D‐glucose catalyzed by xylose isomerase from Thermotoga naphthophila RKU ‐10
Author(s) -
Fatima Bilqees,
Aftab Muhammad Nauman,
Haq Ikramul
Publication year - 2021
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/jctb.6819
Subject(s) - chemistry , xylose isomerase , isomerization , xylose , isomerase , kinetics , fructose , d glucose , reaction rate constant , catalysis , stereochemistry , enzyme , fermentation , biochemistry , physics , quantum mechanics
BACKGROUND Aldo‐keto isomerizations of D‐xylose and D‐glucose catalyzed by xylose isomerase (XI) is commercially carried out to produce bio‐ethanol and high fructose corn syrup. XI is a metalloenzyme. In this paper, kinetics and thermodynamics of the activity and stability of hyperthermophilic recombinant XI from Thermotoga naphthophila RKU‐10 T (TnapXI) were studied in the presence and absence of metal ions. RESULTS Kinetics parameters of recombinant XI from TnapXI were calculated as K m = 0.99 mmol L –1 , V max = 500 μmol.mg −1 .min −1 , and k cat = 68.3 min −1 for the isomerization of D‐xylose (aldo) ⇌D‐xylulose (keto) , whereas for D‐glucose (aldo) ⇌D‐fructose (keto) conversion K m = 7.72 mmol L –1 , V max = 90 μmol.mg −1 .min −1 , and k cat = 12.4 min −1 . Ionization constants were calculated as pK a1 = 6.0 and pK a2 = 7.6, whereas activation constants ( K a ) of TnapXI were 0.3, 0.5, and 4.0 mmol L –1 for Co 2+ , Mn 2+ , and Mg 2+ , respectively. Inhibition constant ( K i ) was 0.119 mmol L –1 for Ca 2+ . Q 10 was 2.8 and E a = 82.25 kJ.mol −1 . Thermodynamics for isomerization were calculated as ∆ H * = 79.2 kJ.mol −1 , ∆ G * = 83 kJ.mol −1 , and ∆ S * = −10.5 J.mol −1 .K −1 . The z ‐value was 12.6 °C for apo‐TnapXI and 32.6 °C for holo‐TnapXI. Deactivation parameters were ∆ G * (d) = 100 kJ.mol −1 , ∆ H * (d) = 206 kJ.mol −1 , ∆ S * (d) = 0.28 kJ.mol −1 .K −1 for apo‐TnapXI and t 1/2 = 18 min at 95 °C, while ∆ G * (d) = 104 kJ.mol −1 , ∆ H * (d) = 767 kJ.mol −1 , ∆ S * (d) = 1.8 kJ.mol −1 .K −1 for holo‐TnapXI and t 1/2 = 65 min at 95 °C. CONCLUSION These noteworthy features make this enzyme an attractive candidate for the industrial production of fuel ethanol and high fructose corn syrup at high temperatures to maximize the product yield. © 2021 Society of Chemical Industry (SCI).