Mörtberg M, Neujahr H Y
Biochem Biophys Res Commun. 1987 Jul 15;146(1):41-6. doi: 10.1016/0006-291x(87)90687-5.
The half saturation constant for phenol was much lower with phenol hydroxylase in situ than with the purified enzyme, whereas the constant for NADPH was higher. In both cases, the linearized plots of the Michaelis-Menten equation were biphasic and the half saturation constants for all phenolic substrates were several times lower, when the phenol was added to the assay medium before NADPH, than when NADPH was added first. There was a similar, but much smaller, effect on the half saturation constants for NADPH. The V-values were not affected by the order of addition. The results suggest slow conformational changes in the enzyme during the overall reaction, which seem even slower, when the enzyme is measured in situ.
苯酚羟化酶原位催化时，苯酚的半饱和常数比纯化酶时低得多，而NADPH的半饱和常数则较高。在这两种情况下，米氏方程的线性化图均为双相，且当在NADPH之前将苯酚添加到测定介质中时，所有酚类底物的半饱和常数比先添加NADPH时低几倍。对NADPH的半饱和常数也有类似但小得多的影响。V值不受添加顺序的影响。结果表明，在整个反应过程中酶存在缓慢的构象变化，而在原位测量酶时，这种变化似乎更慢。
