Department of Agricultural Chemistry, School of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422, Japan.
Plant Physiol. 1978 Nov;62(5):826-30. doi: 10.1104/pp.62.5.826.
Cold lability of pyruvate, orthophosphate dikinase was investigated using a homogeneous, purified enzyme preparation from maize (Zea mays L. var. Golden Cross Bantam T51) leaves. Its stability was markedly reduced below about 10 C and the rate of cold inactivation followed first order kinetics at a concentration lower than about 0.1 milligram of enzyme per milliliter. Cold inactivation was little affected by pH in the range which gives good stability for the enzyme at warm temperatures and the enzyme activity was protected strongly by inclusion of substrates (pyruvate and phosphoenolpyruvate) and polyols such as sucrose, sorbitol, and glycerol. Loss of catalytic activity was accompanied by an apparent dissociation of a tetrameric form of the enzyme (9S form) into a new, more slowly sedimenting (5.1S) component. Inclusion of pyruvate at 4 mM in the cold-treated enzyme had no effect on the sedimentation value. A sharp change in activation energy of the dikinase-catalyzed reaction was observed near 12 C and its break point appears to be close to the generally accepted critical low temperature limit for the growth of maize plants.
采用来自玉米（Zea mays L. var. Golden Cross Bantam T51）叶片的均质、纯化酶制剂研究了丙酮酸-1，5-二磷酸激酶的冷不稳定性。其稳定性在约 10°C 以下明显降低，在低于约 0.1 毫克/毫升的浓度下，冷失活遵循一级动力学。在低温下对酶具有良好稳定性的 pH 范围内，冷失活受 pH 的影响很小，并且通过包含底物（丙酮酸和磷酸烯醇丙酮酸）和多元醇（如蔗糖、山梨糖醇和甘油）强烈保护酶的活性。催化活性的丧失伴随着酶的四聚体形式（9S 形式）明显解离为新的、沉降速度较慢（5.1S）的组分。在冷处理的酶中包含 4mM 的丙酮酸对沉降值没有影响。在约 12°C 附近观察到二激酶催化反应的活化能发生急剧变化，其断点似乎接近通常接受的玉米植株生长的临界低温下限。
