A reusable catalyst was prepared with heat treated whole microbial cells of $\underline{Streptomyces}$ by extrusion into small pieces of particulate cell aggregates, followed by glutaraldehyde treatment as a cross-linking agent for the continuous isomerization process.
$\underline{Streptomyces sp}$. K-45 was screened from soil, which produced relatively high enzyme activity and very stable in high temperature when it was cultured in the medium containing xylose as an enzyme inducer. Cultured cells were treated with heat of 65℃ for 15 min to improve the stability and recovery of enzyme, which were extruded into small aggregates and enzyme was fixed in the inner side of cell by glutaraldehyde treatment of 5% (w/v) for 3 hr.
Immobilized whole cell products showed 25% of the enzyme activity of that of intact whole cells. This immobilized enzyme preparations showed more broad pH optimum and the same stability against high temperature. In particular, the product showed the good physical strength.
The specific activity and equilibrium conversion of glucose to fructose were 48 units per gram of dried immobilized enzyme and 46%, respectively, in the batch stirred reactor system and 115 units and 55% in the continuous packed bed reactor system.
The operational stability of the immobilized glucose isomerase was observed to show high stability sufficient to be adapted to the continuous reactor, and the thermal inactivation of this enzyme was confirmed to obey the first order decay mode. The decay constant was $4.5×10^{-4}hr^{-1}$ which corresponded to the half life of about 115 days, when it was allowed to catalyze the reaction with 1 M substrate solution at a residence time of 5.3 hr at 65℃.
The overall reaction rate of immobilized glucose isomerase preparation, however was found to be severely limited by internal and external diffusional limitation. The $K_{mf}$ and $V_{mf}$ in the batch reactor system was 0.227 M and 0.255μ moles/min, respectively. In the packed bed reactor, the apparent $K_m$ value varied with the superficial velocity, which illucidated the presence of the external diffusion limitation in the system. As the superficial velocity increased, this value approached the value obtained in batch system.
The packed bed reactor showed good flow properties with the voidage of 0.36 when the packing density was 450 g per liter of reactor volume.
Some parameters affecting the productivity were taken into consideration and 55% of substrate was converted at the condition of 1 M substrate concentration and 80 min of space time. Productivity was found to be dependent on the amount of the enzyme loaded.
비교적 높은 역가의 포도당 이성화 효소를 생산하는 방선균을 토양으로부터 선별하여 그 배양 균체의 직접 고정을 통하여 연속적인 이성화 공정에 적합한 고정화 효소를 제조하고자 하였다.
분리된 균주는 액체 배양시 배양액 1 ml 당 최대 3.5 unit, cell 1g 당 282 unit 의 역가를 보여 주었다. 이 효소의 높은 열 안정성을 이용하여 선택적인 열 처리 과정을 거친뒤 사출하여 입자모양의 균체를 만든후 5 % (W/V) 의 glutaraldehyde 를 가교제로서 3시간 동안 처리함으로써 효소를 고정하였다. 고정화 효소의 수율은 26 \% 였고 수용상의 효소와 비슷한 성질을 보여 주었다. 고정화 효소의 단위 활성역가는 회분식 반응조에서는 1 g 당 48 unit, 충진식 연속 반응조에서는 1 g 당 115 unit 로 나타났으며 물질 전달계수가 반응속도에 중요한 영향을 미치는 것으로 밝혀졌다.
연속적인 공정을 위한 기초 조사로서 충진 반응기에서의 반응 특성을 살펴본 결과 실제 공간율은 0.36 이며 충진 밀도는 450 g/L 이었으며 체제시간 분포를 살펴본 결과 좋은 충진형상을 보여줌을 알았다.
이 효소의 연속 공정중의 활성 감퇴 현상을 고찰하기 위하여 2.5 M 농도의 포도당 용액을 체제시간이 5.3 시간이 되도록 유속을 조절하여 약 220 시간동안 65℃ 에서 작동시켰다. 이로부터 이 효소의 활성 감퇴속도가 일차 반응을 따르며 감퇴상수는 $4.5\times10^{-4} hr^{-1}$ 이고 활성 반감기는 115 일로 연속적인 공정에 이용 가능함을 보여 주었다.
생산성에 영향을 미치는 몇가지 인자들에 대하여 살펴 보았는데 체장시간을 길게 해주면 연속 공정에서 55 % 가량의 포도당이 이성화 될 수 있음을 알았다. 생산성은 또한 반응액의 농도와 통과속도, 반응조의 외형 및 효소의 부하율 등에 영향을 받는다는 것을 알 수 있었다.
