Purvis A C, Tischler C R
Department of Plant Sciences, Texas A&M University, College Station, Texas 77843.
Plant Physiol. 1976 Jul;58(1):95-9. doi: 10.1104/pp.58.1.95.
Germinating cotton (Gossypium hirsutum L. cv. Deltapine 16) cotyledons developed two peaks of in vitro nitrate reductase activity; the first was stable in vitro and appeared 24 hours after imbibition; and the second, which was extremely labile in vitro, began to develop after the seedlings had emerged and developed chlorophyll. Nitrite reductase activity peaked only after the seedlings had emerged. Dowex 1-Cl (10%, w/v) and bovine serum albumin (3%, w/v) significantly improved the activity of extracted enzyme; greater improvement occurred as expansion of the cotyledons progressed. The major effect of bovine serum albumin on nitrate reductase activity in cotyledon extracts appeared to be that of making the extracted enzyme more active rather than increasing the amount of nitrate reductase extracted or improving the stability of the extracted enzyme.Attempts to correlate protease activity with the increasingly labile nitrate reductase activity in expanding cotyledons were unsuccessful. Instead, when extracts containing stable nitrate reductase were mixed with extracts containing labile nitrate reductase, the latter was stabilized. The nature of the "protector" in the stable extracts is not known. It is heat-stable, but apparently does not function in vivo since nitrate reductase in germinating cotton seedlings rapidly declines following a peak of activity at 24 hours. We suggest that the protector may function by preventing nitrate reductase from dissociating into inactive subunits.
萌发的棉花（陆地棉品种岱字棉16）子叶产生了两个体外硝酸还原酶活性高峰；第一个高峰在体外稳定，在吸胀24小时后出现；第二个高峰在体外极不稳定，在幼苗出土并形成叶绿素后开始出现。亚硝酸还原酶活性仅在幼苗出土后达到峰值。Dowex 1-Cl（10%，w/v）和牛血清白蛋白（3%，w/v）显著提高了提取酶的活性；随着子叶的展开，活性提高得更多。牛血清白蛋白对子叶提取物中硝酸还原酶活性的主要作用似乎是使提取的酶更具活性，而不是增加提取的硝酸还原酶的量或提高提取酶的稳定性。试图将蛋白酶活性与展开的子叶中越来越不稳定的硝酸还原酶活性相关联的尝试未成功。相反，当含有稳定硝酸还原酶的提取物与含有不稳定硝酸还原酶的提取物混合时，后者会稳定下来。稳定提取物中“保护剂”的性质尚不清楚。它是热稳定的，但显然在体内不起作用，因为萌发的棉花幼苗中的硝酸还原酶在24小时达到活性峰值后迅速下降。我们认为保护剂可能通过防止硝酸还原酶解离成无活性的亚基而起作用。
