Orthophosphate anion enhances the stability and activity of endoxylanase from Bacillus sp.
Endoxylanase, for which the optimum temperature is 60 degrees C (optimum pH 7), is labile to heat. Because the isoelectric point (pI) value of this xylanase is 10.6, the net charge of this enzyme is positive at pH 7. Thus, ions are likely to influence its enzyme structure and the thermal stability of endoxylanase may improve. Among the various ions tested, orthophosphate anion (HPO(4)(2-)) was found to significantly improve not only the stability but the activity of xylanase. When K(2)HPO(4) concentration was increased from 50 mM to 1.2 M, the T(m )value of xylanase was increased from 60.0 degrees C to 74.5 degrees C. The affinity of xylanase on xylan also increased along with K(2)HPO(4) concentration. Thus, the xylanase activity at 0.6 M K(2)HPO(4) was 2.3-fold higher than that at 50 mM K(2)HPO(4), and 120.2-fold higher than that in 40 mM MOPS buffer. This enhanced activity in the presence of K(2)HPO(4 )probably takes place because the orthophosphate anion affects the binding and catalytic residues of endoxylanase.
Park
M T
MT
Department of Biological Sciences, Korea Advanced Institute of Science and Technology 373-1, Kusong-Dong, Yusong-Gu, Taejon 305-701, Korea.
Lee
M S
MS
Choi
J Y
JY
Kim
S C
SC
Lee
G M
GM
D000838:Anions / Q000494:pharmacology; D001407:Bacillus / Q000187:drug effects / Q000201:enzymology*; D001426:Bacterial Proteins / Q000378:metabolism*; D001665:Binding Sites / Q000187:drug effects; D020134:Catalytic Domain / Q000187:drug effects; D002412:Cations / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D043364:Endo-1,4-beta Xylanases; D018698:Glutamic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D007700:Kinetics; D009994:Osmolar Concentration; D010710:Phosphates / Q000494:pharmacology*; D017680:Potassium Compounds / Q000494:pharmacology; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014995:Xylosidases / Q000378:metabolism*
D000838:Anions; D001426:Bacterial Proteins; D002412:Cations; D010710:Phosphates; D017680:Potassium Compounds; D018698:Glutamic Acid; C013216:potassium phosphate; D014995:Xylosidases; D043364:Endo-1,4-beta Xylanases