Characterization of Acidic Nucleotidase from Aspergillus niger

Aspergillus niger의 Acidic Nucleotidase의 특성

Acidic nucleotidase from Asfiergilius nlger has been partially purified by Sepharose CL-6B gel filtration and DEAE-Sephacel ion exchange chromatography. The optimum pH and temperature for the enzyme reaction with 5'-AMP or 3'-AMP as a substrate were 4.5 and 55%, respectively. However, the optimum temperature became 70% when p-nitrophenyl phosphate was used as a substrate. The enzyme was stable at acidic pH. The enzyme activity was not affected by addition of various nucleotides, nucleosides and inorganic phosphates. Ferric, aluminium, vanadate and molybdate ions inhibited the enzyme activity dramatically. In kinetic studies, $K_m$), values for 3'-AMP, 5'-AMP and p-nitrophenyl phosphate were 1.39 mM, 1.5 mM and 5.77 mM, respectively. The substrate efficiency ($V_{max}/K_m$) shows 3'-AMP is the prefered substrate for the enzyme among tested substrates.

Aspergillus niger로부터 acidic nucleotidase를 Sepharose CL-6B gel 여과와 DEAE-Sephacel 이온교환수지를 이용하여 부분정제하였다. 5'-AMP 와 3'-AMP를 기질로 사용했을 경우에 효소의 최적 pH는 4.5, 그리고 최적온도는 $55^{\circ}C$였다. 그러나, p-nitrophenyl phosphate를 기질로 사용했을 경우에는 최적 pH는 변화가 없었으나, 최적 온도는 $70^{\circ}C$였다. 효소의 활성화에너지는 3'-AMP, 5'-AMP 그리고 p-nitrophenyl phosphate를 기질로 사용했을 경우에 각각 4.76kcal/mole, 6.95kcal/mole 그리고 11.82kcal/mole 였다.