大豆苗中硝酸還原酵素—受質誘導合成，酵素純化及其性質

Abstract

1．大豆苗經1 mM硝酸鈣誘導處理3小時後，硝酸還原酵素活性可達於最高。 2．大豆苗硝酸還原酵素，在標準測定情況下，其最適酸度是7.2；最適溫度是27℃。酵素對受質的Km是4.6×10-4M 3．粗酵素經硫胺沉澱法，磷酸鈣膠法及DEAE-cellulose gel法純化後，可獲17.2倍之純化效果，是遠較Schrader等（1968）所得100倍為小。其原因在繼續追究中。 4．適當濃度之有機含硝基化合物可誘導此酵素的新的合成，惟其誘導機構可能與無機硝酸鹽的誘導者不同。 5．在暗室中生長的大豆苗，Kinetin可刺激酵素的誘導合成作用；Indole-3-Acetic Acid及Gibberellic Acid無影響。光照下生長的大豆苗，外加之植物荷爾蒙時無影響。

Nitrate reductase (E.C. 1661) in soybean seedlings was partially purified and characterized. Its synthesis and/or activity by the effects of inorganic nitrate, organic nitro-compounds (chloramphenicol, N, N'-dinitroethylene diamide, -nitroaniline, 2,4-dinitrophenol) and plant hormones have been studied. By means of ammonia sulfate fractionations, calcium phosphate gel batch, and DEAE-cellulose gel batch, the nitrate reductase has been purified about 17-fold. Under the standard assay conditions, the enzyme has optimum pH at 7.2 and optimum temperature at 27 C. Its apparent Km value for nitrate is 4,6 × 10-4 M. Exogeneously applied organic nitro-compounds, as inorganic itrate, show approximately the same extent of induction of trate reductase synthesis. Because of their additive effects the induction of nitrate reductase synthesis, the action Lechanisms of organic nitro-compounds and inorganic nitrate may be somehow different. Kinetin apparently stimulates the substrate induction of nitrate reductase in dark grown soybean seedlings, but Gibberellic acid and Indole-3-acetic acid do not. Furthermore, the effect of kinetin could be significantly evident within 3 hours after application. The possible physiological role of kinetin stimulation is discussed.