Bowien B, Gottschalk E M
J Biol Chem. 1982 Oct 25;257(20):11845-7.
Ribulose-1,5-bisphosphate carboxylase from the chemolithotrophic hydrogen bacterium Alcaligenes eutrophus was maximally active in the presence of 50 mM HCO3- plus 10 mM Mg2+. Deactivation occurred upon removal of these ions. Reactivation was achieved by incubation of the enzymes with HCO3- plus Mg2+. The concentration of HCO3- (CO2) required for half-maximal activation was 1.84 nM (0.064 mM). Sedimentation velocity studies revealed that activation/deactivation is associated with drastic changes in the sedimentation properties of the enzyme. While the inactive form had a sedimentation coefficient, s20,w, of 17.5 S, the s20,w gradually decreased as the enzyme was reactivated and the fully reactivated form exhibited an s20,w of 14.3 S. A structural analogue of ribulose 1,5-bisphosphate, xylulose 1,5-bisphosphate, caused a deactivation of the enzyme concomitant with an increase in the sedimentation velocity. It is suggested that the alterations in the hydrodynamic properties accompanying the activation/deactivation process are due to considerable conformational changes that affect the molecular volume and/or the shape of the enzyme. Dissociation/association events were not involved in the changes. The s20,w of about 18 S, generally reported for the large hexadecameric ribulose bisphosphate carboxylases, appears to be characteristic of the inactive form.
自嗜碱产碱杆菌这种化能无机营养型氢细菌中提取的1,5-二磷酸核酮糖羧化酶，在存在50 mM HCO₃⁻加10 mM Mg²⁺的情况下活性最高。去除这些离子后酶会失活。通过将酶与HCO₃⁻加Mg²⁺一起孵育可实现再激活。半最大激活所需的HCO₃⁻（CO₂）浓度为1.84 nM（0.064 mM）。沉降速度研究表明，激活/失活与酶沉降特性的剧烈变化有关。无活性形式的沉降系数s₂₀,w为17.5 S，随着酶的再激活，s₂₀,w逐渐降低，完全再激活形式的s₂₀,w为14.3 S。1,5-二磷酸核酮糖的结构类似物1,5-二磷酸木酮糖会导致酶失活，同时沉降速度增加。有人提出，激活/失活过程中伴随的流体动力学性质的改变是由于影响酶分子体积和/或形状的显著构象变化所致。解离/缔合事件与这些变化无关。通常报道的大约18 S的s₂₀,w似乎是无活性形式的特征。
