一些栽培作物的核酮糖-1,5-二磷酸羧化酶/加氧酶动力学特征

SPECIES VARIATION IN THE KINETIC PROPERTIES OF RIBULOSE-1, 5-BISPHOSPHATE CARBOXYLASE/OXYGENASE

在相同条件下,对C_2植物中的9种双子叶植物和3种单子叶植物的核酮糖-1,5-二磷酸羧化酶/加氧酶(Rubisco)动力学特性进行了测定。K_m(CO_2)(K_c)和K_m(O_2)(K_(?))的变化范围分别为7.3～30μmol/L和300～1000μmol/L。变异系数分别为52％和38％。K_c值的变异明显高于K_o值。V_(max)(CO_2)(V_c)和V_(max)(O_2)(V_(?))分别为50～1500和16～500n mol/mg酶蛋白·min,变异系数相应为97％和87％。专一性因子的变化相对较小,为78～121,变异系数为15％。说明在C_3植物中,Rubisoo动力学特性的差异主要反应在V_(max)值上,核酮糖-1,5-二磷酸羧化酶(Rubisc)的动力学特性变化大于核酮糖-1,5-二磷酸加氧酶(Rubiso)。随着物种的进化,K_c、K_o值明显降低,而V_c、V_o值显著增加,致使Rubisco活性显著提高。Rubisco的羧化/加氧比也依物种的进化而上升。K_c与K_o、V_c与V_o之间具有显著的同步变化趋势,相关系数均超过极显著水平。

The kinetic properties of Rubisco purified from 12 species of C3 plants (3 species of monocotyledon plants and 9 species of dicotyledon plants) were determined under standard condition of activation and assay. Km (CO2) values ranged from 7. 3 to 30 μmol/L. Km (O2) values ranged from 300 to 1 000 μmol/L. The variation coefficients of Km (CO2) and Km (O2) were 52% and 38%, respectively. The variation of Km (CO2) was significantly higher than that of Km (O2). The values of Vman(CO2) and Vmax (O2) ranged from 50 to 1 500, and from 16 to 500 n mol/ mg enzyme protein ·22 min, the variation coefffciets were 97% and 87%, respectively. These results showed that, in C2 plants, the variations of the kinetic properties of ribulose-1, 5-bisphosphate carboxylase/oxygenase existed mainly in the values of Vmax and in RuBP carboxylase.No difierences in the ratio of either Km (CO2) /Xm (O2) or Vmax (CO2) /Vmax (O2) were detected among the Rubisco enzymes from these C2 plants. But, the results of correlation analysis showed that significant correlativity existed between Km (CO2) and Km (O2), as well as between Vmax (CO2) and Vmax (O2). The correlation coefficients were 0. 700 and 0. 923, respectively. The variations of the kinetic properties of RuBP carboxylase and oxygenase were synchronous.The specificity lacton were more stable than other kinetic constants, and ranged from 78 to 121, variation coefficient was 1.5%.