Abstract
Catechol 2,3-dioxygenase was purified from recombinant strain E. coli CNU312 carrying the tomB gene which was cloned from toluene-degrading Burkholderia cepacia G4. The purification of this enzyme was performed by acetone precipitation, Sephadex G-75 chromatography, electrophoresis and electro-elution. The molecular weight of native enzyme was about 140.4 kDa and its subunit was estimated to be 35 kDa by SDS-PAGE. It means that this enzyme consists of four identical subunits. This enzyme was specifically active to catechol, and$K_(m)$ value and $V_(max)$value of this enzyme were 372.6 $\mu$M and 39.27 U/mg. This enzyme was weakly active to 3-methylcatechol, 4-methylcatechol, and 4-chlorocatechol, but rarely active to 2,3-DHBP. The optimal pH and temperature of the enzyme were pH 8.0 and $40^{\circ}C$. The enzyme was inhibited by $Co^(2+)$, $Mn^(2+)$, $Zn^(2+)$, $Fe^(2+)$, $Fe^(3+)$, and $Cu^(2+)$ ions, and was inactivated by adding the reagents such as N-bromosuccinimide, and $\rho$-diazobenzene sulfonic acid. The activity of catechol 2,3-dioxygenase was not stabilized by 10% concentration of organic solvents such as acetone, ethanol, isopropyl alcohol, ethyl acetate, and acetic acid, and by reducing agents such as 2-mercaptoethanol, dithiothreitol, and ascorbic acid. The enzyme was inactivated by the oxidizing agent $H_(2)$$O_(2)$, and by chelators such as EDTA, and ο-phenanthroline.
Toluene, phenyl 등의 분해균주인 Burkholderia cepacia G4로부터 tomB 유전자를 클로닝하여 얻은 재조합 균주 E. coli CNU312로부터 catechol 2,3-dioxygenase를 정제하여 효소학적 특성을 조사하였다. Catechol 2,3-dioxygenase는 native 분자량이 약 140.4 kDa이었으며 4개의 동일한 35 kDa subunit로 구성된 homotetramer로 생각된다. Catechol의 $K_(m)$값과 $V_(max)$값은 372.6 $\mu$M과 39.27 U/mg이었으며, 1.56 mM 이상의 기질 농도에서는 활성이 감소되었다. 효소 활성의 최적 pH는 8.0이었으며, pH 7.0-8.0 범위에서 안정하였다. 최적 활성온도는 $40^{\circ}C$였으며, $60^{\circ}C$이상에서 완전히 활성을 상실하였다. 또한 $Fe^(2+)$, $Fe^(3+)$ 를 비롯한 대부분의 금속 이온에 의해 활성이 감소되었으며, $Mg^(2+)$, $K^(+)$에는 영향을 받지 않았다. 효소 활성부위를 알아보기 위해 화학변형제를 처리한 결과, tryptophan과 histidine이 효소 활성부위에 존재하는 것으로 추정된다. 그리고 10%의 유기용매에 안정성을 보이지 않았으며, $H_(2)$$O_(2)$, EDTA, ο-phenanthroline에도 활성이 감소되었다. 또한 2-mercaptoethanol, dithiothreitol, 그리고 ascorbic acid와 같은 환원제에 대해서도 안정성을 보이지 않았다. 이 효소는 catechol에 대해 높은 기질 특이성을 보였으며, 3-methylcatechol, 4-methylcatechol, 그리고 4-chlorocatechol에 대해 약간의 활성을 보였다. 그러나 2,3-dihydroxybiphenyl에 대해서는 거의 활성을 보이지 않았다.
