Aspergillus sp.가 생산하는 Glucoamylase Isozymes의 성질

Properties of Glucoamylase Isozymes Produced by Aspergillus sp.

Aspergillus sp.로부터 추출한 glucoamylase를 Sephacryl S-200과 DEAE-Sephacel 이온교환 칼럼을 통과시킨 후, 2개의 Isozyme으로 분리하였다. 분리된 glucoamylase isozyme(GI, GII)의 효소학적특성을 각각 조사하였다. GI 및 GII isozyme의 활성최적 pH 및 온도는 pH4.5 및 <TEX>$65^{circ}C$</TEX>였다. 분리된 효소는 pH 3-7 사이에서 안정했으며, 또한 55<TEX>$^{circ}C$</TEX> 이하에서 안정하였다. Hg<TEX>$^{++}$</TEX>는 효소 황성을 완전히 저해하였으나, 글리세롤은 효소의 안정성을 크게 증가시켰다. 효소반응의 활성화에너지는 GI의 경우 10,62 kcal/mole이었으며, GII의 경우에는 10.23kcal/mole이었다. GI isozyme의 기질에 대한 Km값은, 0.62% (soluble starch), 0.32% (dextrin), 1.03%(glycogen)이었으며, GII isozyme의 경우에는, 0.66%(soluble starch) 0.23%(dextrin), 그리고 0.14% (glycogen)이었다.

Glucoamylase (EC 3.2.1.3) of Aspergillus sp. isolated from soil was partially purified by Sephacryl S-200 gel filtration and DEAE-Sephacel ion exchange chromatography, The glucoamylase activity was separated into two isozymes after DEAE-Sephacel ion exchange chromatrography. The optimum pH and temperature for both glucoamylase isozymes (GI, GII) were identical; pH 4.5 and temperature, <TEX>$65^{circ}C$</TEX>. The molecular weights of GI and GII Isozymes were estimated to be 105,000, which were measured by gel filtration on Sephacryl S-200. Both isozymes were stable at pH ranges of 2 to 7, and up to 6<TEX>$0^{circ}C$</TEX>. Glycerol was effective to stabilize the both isozymes. The activation energies of GI and GII isozymes were 10.63 and 10.33 kcal/mole, respectively. The enzyme activities of both isozymes were completely inactivated by addition of 0.1% Hg<TEX>$^{++}$</TEX>. In kinetic studies, the Km values of GI isozyme for soluble starch, dextrin, and glycogen were 0.62%, 0.32%, and 1.02%, respectively. For GII isozyme, they became 0.66%, 0.23%. and 0.14% for the substrates.