Chong A K, Pegg M S, von Itzstein M
School of Pharmaceutical Chemistry, Victorian College of Pharmacy, Australia.
Biochim Biophys Acta. 1991 Mar 8;1077(1):65-71. doi: 10.1016/0167-4838(91)90526-6.
Ca2+ increases the initial rate of activity of sialidase from influenza virus (A/Tokyo/3/67). Increasing ionic strength also activates influenza virus sialidase. When ionic strength is controlled, smaller but still significant Ca2+ effects are observed, with Vmax/Km increased from 0.8.10(5) to 1.4.10(5) M-1 s-1 and Vmax increased from 6.3 to 9.5 s-1 by saturating Ca2+. The Ki of the competitive inhibitor 2,3-dehydro-2-deoxy-N-acetylneuraminic acid was decreased from 2.7.10(-6) to 1.15.10(-6) M after the addition of saturating Ca2+. The data show that Ca2+ exerts a specific effect on Vmax/Km, leading to an increased rate of interaction of substrate with the enzyme. The Kd-app for the Ca2(+)-sialidase complex is 2 mM. Except for Mg2+ which behaves similarly to Ca2+, other mono- and divalent cations have little specific effect on sialidase kinetics. Sequence analysis of a range of subtypes of sialidases from influenza virus supports the proposal that Ca2+ binds at the subunit interface transmitting a conformational change to the enzyme active site. Ca2+ activation may have a physiological role in switching on sialidase activity during the release of newly synthesised virions from the host cell surface.
钙离子可提高流感病毒（A/东京/3/67）唾液酸酶的初始活性速率。增加离子强度也可激活流感病毒唾液酸酶。当离子强度得到控制时，仍可观察到较小但仍显著的钙离子效应，通过加入饱和钙离子，Vmax/Km从0.8×10⁵ M⁻¹ s⁻¹增加到1.4×10⁵ M⁻¹ s⁻¹，Vmax从6.3 s⁻¹增加到9.5 s⁻¹。加入饱和钙离子后，竞争性抑制剂2,3-脱氢-2-脱氧-N-乙酰神经氨酸的Ki从2.7×10⁻⁶ M降至1.15×10⁻⁶ M。数据表明，钙离子对Vmax/Km有特定影响，导致底物与酶的相互作用速率增加。Ca²⁺-唾液酸酶复合物的表观解离常数Kd-app为2 mM。除了与钙离子表现相似的镁离子外，其他单价和二价阳离子对唾液酸酶动力学几乎没有特定影响。对一系列流感病毒唾液酸酶亚型的序列分析支持了这样的观点，即钙离子在亚基界面结合，向酶活性位点传递构象变化。钙离子激活可能在新合成的病毒粒子从宿主细胞表面释放过程中开启唾液酸酶活性方面具有生理作用。
