Martel P, Powell B M, Johnston R A, Petkau A
Biochim Biophys Acta. 1983 Sep 14;747(1-2):78-85. doi: 10.1016/0167-4838(83)90124-3.
The approximate size and shape of holo and apo forms of bovine cupro-zinc erythrocyte superoxide dismutase (EC 1.15.1.1) were determined by small-angle neutron scattering from aqueous solutions at neutral pH. A model assuming a cylindrical shape gave the best fit to the data for both forms of the enzyme. The radius of gyration, Rg, of the apoenzyme was found to be marginally larger than that of the holoenzyme. Scattering from the protein vanished for H2O/2H2O mixtures containing 42(+/- 2)% 2H2O, and the negligible dependence of Rg on the 2H2O fraction indicated uniform scattering density. Irradiation with 60Co gamma-rays resulted in aggregation of superoxide dismutase molecules; scattering at small doses was interpreted in terms of pairwise side-by-side aggregation. For large doses (approx. 3.8 X 10(3) Gy) and at relatively high enzyme concentrations (320 microM), the interpretation of the neutron scattering data is ambiguous. The value of Rg suggests that end-to-end stacking of the cylindrical molecules is one possibility. The equilibrium concentration of separated subunits was found to be unobservable and calculations showed that denaturation did not contribute significantly to our neutron scattering measurements for the radiation doses employed (maximum 3.8 X 10(5) Gy). High-performance liquid chromatography (HPLC) data showed that in mixtures the apo and holo forms of superoxide dismutase interact with one another, and that the side-by-side aggregates, induced by irradiation of the enzyme, are readily dissociated, resulting in a single elution peak that is resolved from the later peak common to both the apo and holo forms.
通过在中性pH值下对水溶液进行小角中子散射，测定了牛铜锌红细胞超氧化物歧化酶（EC 1.15.1.1）全酶和脱辅基酶形式的大致尺寸和形状。一个假设为圆柱形的模型对两种酶形式的数据拟合效果最佳。发现脱辅基酶的回转半径Rg略大于全酶的回转半径。对于含有42（±2）% 2H2O的H2O/2H2O混合物，蛋白质的散射消失，且Rg对2H2O分数的依赖性可忽略不计，这表明散射密度均匀。用60Co γ射线辐照导致超氧化物歧化酶分子聚集；小剂量辐照下的散射可通过两两并排聚集来解释。对于大剂量（约3.8×10³ Gy）且酶浓度相对较高（320 μM）时，中子散射数据的解释存在歧义。Rg值表明圆柱形分子端对端堆叠是一种可能。发现分离的亚基的平衡浓度不可观测，计算表明变性对我们所采用的辐射剂量（最大3.8×10⁵ Gy）的中子散射测量没有显著贡献。高效液相色谱（HPLC）数据表明，在混合物中，超氧化物歧化酶的脱辅基酶形式和全酶形式相互作用，并且酶辐照诱导的并排聚集体很容易解离，产生一个单一的洗脱峰，该峰与脱辅基酶形式和全酶形式共有的较晚峰分开。
