Harpel M R, Hartman F C
Protein Engineering Program, Oak Ridge National Laboratory, Tennessee 37831-8077.
J Biol Chem. 1992 Apr 5;267(10):6475-8.
The CO2/O2 specificity factor of ribulose-bisphosphate carboxylase/oxygenase partially determines the efficiency of photosynthetic carbon assimilation. Heretofore, engineered alterations of the enzyme have only decreased the selectivity for CO2 utilization. We show that alanyl replacement of active-site Ser-368 of the Rhodospirillum rubrum carboxylase enhances the carboxylation selectivity approximately 1.6-fold over the wild-type level. This enhancement reflects a greater relative decline in oxygenase efficiency than in carboxylase efficiency. In contrast to wild-type enzyme, the carboxylase activity of the Ser-368 mutant protein is not perceptibly inhibited by O2, perhaps indicative of a change in rate-limiting steps in the overall reaction pathway.
1,5 - 二磷酸核酮糖羧化酶/加氧酶的CO₂/O₂特异性因子部分决定了光合碳同化的效率。迄今为止，对该酶进行的工程改造仅降低了对CO₂利用的选择性。我们发现，用丙氨酸替换红螺菌羧化酶活性位点的丝氨酸368，其羧化选择性比野生型水平提高了约1.6倍。这种提高反映出加氧酶效率的相对下降幅度大于羧化酶效率。与野生型酶不同，丝氨酸368突变蛋白的羧化活性不会被O₂明显抑制，这可能表明整个反应途径中限速步骤发生了变化。
