Abstract
In this study, the characterization of purified erythritol 4-phosphate dehydrogenase, key enzyme of erythritol biosynthesis, produced by Penicillium sp. KJ81 was investigated. Optimum production conditions of erythritol 4-phosphate dehydrogenase was 1 vvm areration, 200 rpm agitation, at $37^{\circ}C$ for 8 days in the medium containing 30% sucrose, 0.5% yeast extract, 0.5% $(NH_4)_2SO_4$, 0.1% $KH_2PO_4$, and 0.05%$MgCl_2$. Erythritol 4-phosphate dehydrogenase was purified through ultrafiltration and preparative gel electrophoresis from cell extract of Penicillium sp. KJ81. This enzyme was especially active on erythrose 4-phosphate with 1.07 mM of Km value. It gave a single band on native polyacrylamide gel electrophoresis and an isoelectric point of 4.6. The enzyme had an optimal activity at pH 7.0 and $30^{\circ}C$. It was stable between pH 4.0 and 9.0, and also below $30^{\circ}C$. The enzyme activity was completely inhibited by 1mM $Cu^{2+}$ and 1 mM $Zn^{2+}$, but was not significantly affected by other cations tested. This enzyme was inactivated by treatment of tyrosine specific reagent, iodine and tryptophan specific reagent, N-bromosuccinimide. The substrate of the enzyme, erythrose 4-phosphate showed protective effect on the inactivation of the enzyme by both reagents. These results suggest that tryptophan and tyrosine residues are probably located at or near active site of the enzyme.
Erythritol 생합성에 중요한 효소인 erythritol 4-phosphate dehydrogenase를 Penicillium sp. KJ81로부터 분리 정제하여 효소의 특성을 조사한 결과 다음과 같은 결론을 얻었다. Erythritol 4-phosphate dehydrogenase의 최적 생산 조건은 30% sucrose, 0.5% yeast extract, 0.5% $(NH_4)_2SO_4$, 0.1% $KH_2PO_4$ 그리고 0.05% $MgCl_2$ (pH 7.0) 배지에서 1 vvm aeration, 교반속도 200 rpm, $37^{\circ}C$로 Penicillium sp. KJ81을 배양한 결과 8일 배양 시 최대의 생산량을 보였다. Penicillium sp. KJ81주의 균체 추출액으로부터 ultrafiltration, 조제용 disc gel electrophoresis를 이용하여 erythritol 4-phosphate dehydrogenase를 분리 정제하였다. 최종 수율은 33%이었으며 정제배수는 39.5였다. 정제된 효소의 pI값은 4.6으로, erythrose 4-phosphate에 특이적으로 반응하였으며, Km값은 1.07mM이었다. Native-PAGE에서 single band를 보인 효소의 분자량은 약 1,500 kDa이었다. 효소활성의 최적 pH와 온도는 pH 7.0, $30^{\circ}C$였으며, 효소는 pH 4.0~9.0, 그리고 $30^{\circ}C$까지 안정하였다. 다양한 금속이온 중 $Cu^{2+}$, $Zn^{2+}$에 의하여 효소의 활성이 저해되었다. 다양한 아미노산 반응 잔기 변형시약 중 iodine과 NBS에 의해 효소의 활성이 저해되는 것을 확인하였다.
