Lehrstuhl für Allgemeine Botanik, Arbeitsgruppe Biochemie der Morphogenese, Ruhr-Universität Bochum, Postfach 102148, D-4630, Bochum 1, Federal Republic of Germany.
Planta. 1977 Jan;136(3):221-8. doi: 10.1007/BF00385988.
Kinetic parameters of the glyoxysomal and mitochondrial malate dehydrogenase (EC 1.1.1.37) of watermelon (Citrullus vulgaris Schrad.) cotyledons were compared. The data were obtained by initial rate experiments at pH 8.5 in both directions of the reaction using homogeneous enzyme preparations. Substrate inhibition at physiologically significant concentrations was observed with reduced nicotinamide adenine dinucleotide (NADH) (50% inhibition at 0.65 mmol·l(-1) NADH), but not with oxaloacetate, L-malate or oxidized nicotinamide adenine dinucleotide. The inhibition of both isoenzymes by 5'adenosine monophosphate was studied. Inhibition was found to be competitive with respect to NADH and non-competitive with respect to oxaloacetate. The apparent inhibitor constants at 200 μmol·l(-1) of the fixed substrates were 3.2 and 1.6 mmol·1(-1) for NADH, and 3.2 and 5.2 mmol·l(-1) for oxaloacetate with the glyoxysomal and mitochondrial isoenzymes, respectively. The energy of activation was determined for oxaloacetate reduction by glyoxysomal (E a =3.14×10(4)J×mol(-1)) and mitochondrial (E a =4.10×10(4) J x mol(-1)) MDH from Arrhenius plots, which exhibited constant slopes throughout the range of thermal stability.Despite considerable structural differences, the results indicate very similar kinetic behaviour of the glyoxysomal and mitochondrial isoenzymes. The physiological significance of the data are discussed in relation to the gluconeogenic processes occuring in cotyledons during germination.
西瓜（Citrullus vulgaris Schrad.）子叶的乙醛酸体和线粒体苹果酸脱氢酶（EC 1.1.1.37）的动力学参数进行了比较。数据是通过在 pH 8.5 下在反应的两个方向上使用均相酶制剂进行初始速率实验获得的。在生理相关浓度下观察到还原型烟酰胺腺嘌呤二核苷酸（NADH）（NADH 为 0.65 mmol·l(-1) 时抑制 50%）对底物的抑制作用，但对草酰乙酸、L-苹果酸或氧化型烟酰胺腺嘌呤二核苷酸没有抑制作用。还研究了 5'腺苷一磷酸对两种同工酶的抑制作用。发现抑制作用对 NADH 为竞争性，对草酰乙酸为非竞争性。在 200 μmol·l(-1) 的固定底物下，对 NADH 的表观抑制剂常数分别为 3.2 和 1.6 mmol·l(-1)，对草酰乙酸的分别为 3.2 和 5.2 mmol·l(-1)，分别对应乙醛酸体和线粒体同工酶。通过 Arrhenius 图确定了乙醛酸体还原的吉布斯自由能（E a =3.14×10(4)J×mol(-1))和线粒体（E a =4.10×10(4) J x mol(-1)) MDH，该图在整个热稳定性范围内显示出恒定的斜率。尽管存在相当大的结构差异，但结果表明乙醛酸体和线粒体同工酶的动力学行为非常相似。讨论了数据的生理意义，涉及到发芽过程中子叶中发生的糖异生过程。
