Characteristics of Extracellular Endo-Inulinase Produced by Pseudomonas sp.

Pseudomonas sp.의 균체외 Endo-Inulinase 특성

Two forms of extracellular endo-inulinase, designated as PIand P II were resolved from a species of Pseudomonas isolated from soil. Both enzymes were glycoproteins with their carbohydrate content of 15% for PIand 2.4% for P II inulinase. Tryptophan residue was proved to be an essential amino acid for their catalytic activity. The molecular weights of PIand P II were estimated to be 210, 000 and 170, 000, respectively. The activity of the two enzymes was strongly inhibited by p-chloromercuribenzoate but the inhibition was nearly completely offset by the addition of the reducing agents such as cysteine or dithiothreitol. On the other hand, the two enzymes were activated about 50-60% of their activities by the presence of Co$^{+2}$ ion, and quite stable at pH values ranging from pH 4.0 to 1.5. They also appeared to be relatively thermostable, and no appreciable inactivation was observed after incubation at 55$^{\circ}C$ for 2 hours. About 70 % hydrolysis rate with PIand 56 % with P II were achieved when inulin was hydrolyzed at 5$0^{\circ}C$ for 12 hours with 60 units of the enzymes in 2 % inulin solution.

토양분리균 Pseudomonas sp.가 생산하는 inulinase를 분리.정제하여 얻은 단일 단백질 효소 PI과 PII는 탄수화물 함량이 각각 15%와 2.4%인 당 단백질 형태의 endo-inulinase로서 두 효소가 모두 촉매활성에 필수적인 tryptophan 잔기를 가지고 있었다. 분자량은 PI 210,000, PII 170,000으로 측정되었다. 1mM pCMB 존재에 의해 두 효소가 약80% 정도의 활성저해를 보였으나 5mM cysteine 또는 1mM dithiothreitol을 첨가하면 효소활성이 거의 완전 회복되는 특성을 나타내었다. 최종 가수분해산물인 fructose(1mM)에 의해 PI, PII 효소가 각각 15% 정도의 활성저해를 받는 반면 Co$^{+2}$ 이온은 50~60%의 높은 활성화 효과를 보였다. 두 효소는 pH 4.0~7.5사이에서 매우 안정하였으며, 열에 대하여서도 비교적 안정하여 6$0^{\circ}C$, 120분 가열에 의해 PI이 약 27%, PII가 약 40%의 실활을 나타낼 뿐이다. 또한 60units의 효소를 사용, 2% inulin을 5$0^{\circ}C$에서 72시간 가수분해 시켰을 때 PI약 70%, PII약56%의 기질 분해율을 보였다.