쌀의 도정 과정 중 얻어지는 미강으로부터 lipoxygenase를 분리, 정제하였으며 이 효소가 지닌 과산화 반응의 촉매작용 특성에 관하여 연구 검토하였다. 이 효소의 분자량은 약 100,000 daltons 이었으며 효소의 등전점 (pI) 값은 4.8로 얻어졌다. 이 효소는 상온하에서는 비교적 안정성을 보이고 있으나 $50^{circ}C$ 이상에서는 상당한 불활성화 현상을 일으키고 있었으며, 이 경우 온도 변화에 따른 불활성화 상수값 $(K_d)$은 40, 50 및 $60^{circ}C$에서 각각 0.002, 0.014 및 0.136 $min^{-1}$로 얻어졌다. 이 효소가 지닌 기질 특이성은 대두 효소에서와 비슷하였으며 리놀레산 기질에 대한 과산화반응의 촉매 활성도는 중성 pH (6.8~7.0)와 $30^{circ}C$에서 최대값을 보였다. 한편 효소 기질간의 친화력은 $K_m$ 값을 비교할 때 리놀레산과 산소분자는 비슷한 값인 약 100 ${mu}M$로서 얻어졌다. 그밖의 효소반응의 초기 속도 측정에 의한 반응 속도론적 실험을 통하여 리놀레산의 과산화반응 양상에 대하여도 고찰해 보았다.
A form of lipoxygenase (EC 1. 13. 11. 12) was isolated from rice brans which were obtained from the milling of rice caryopsis, and was purified partially but to give an electrophoretically homogeneous form. The molecular weight of the enzyme was found to be about 100, 000 daltons based on the gel filtration experiment. The optimum activity for the catalytic hydroperoxidation by rice bran lipoxygenase was obtained at neutural pH (pH 6. 8 to 7. 0) and at $30{^{circ}C$. The enzyme show ed a relative stability under the neutral pH and at room temperature, but a marked deactivation of the enzyme protein was observed at the preincubation temperature above a $50^{circ}C$. The first order deactivation constants for the enzyme were calculated to be 0.002, 4.014, 0.136 and 0.281 per minute at 40, 50, 60 and $70^{circ}C$, respectively. The isoelectric point of the enzyme was about 4. 8 based on the isoelectrofocusing experiment, The enzyme was found to be very specific toward linoleate for the hydroperoxidation as in the case of the soybean enzyme, but the estimated $K_m$ values for linoleate and molecular oxygen were found to be about the same. Based on the steady state kinetic experiment measuring the initial velocity of the enzyme reaction, it was also suggested that the hydroperoxidation of linoleate is proceeded through the formation of a ternary complex between the enzyme and two substrate ligands.
