Momsen W E, Brockman H L
J Biol Chem. 1976 Jan 25;251(2):384-8.
In our two-phase reaction system taurodexycholate prevents the adsorption of pancreatic lipase B to the nonaqueous phase. Our data are consistent with a mechanism for this reaction which involves the cooperative formation of an enzyme-(bile salt)4 complex in solution with a dissociation constant of 1.4 X 10(-15)M4. Whereas the free enzyme is readily adsorbed to a bile salt-substrate-covered surface, the complex is not. Thus, the "inhibition" of substrate hydrolysis occurs because enzyme and substrate are separated physically. The protein cofactor, colipase, reverses the inhibitory effects of bile salt by providing a high affinity binding site at the interface for the lipase-(bile salt)4 complex. Steady state and presteady state kinetic data are consistent with the formation of a complex with a 1/1, lipase/colipase, ratio, and a dissociation constant of 0.4 to 2.8 X 10(-9)M. The rate of adsorption of lipase to adsorbed colipase appears to be controlled by diffusion through the unstirred layer with a second order rate constant of 1.3 X 10(6)M-1S-1.
在我们的双相反应体系中，牛磺去氧胆酸盐可防止胰腺脂肪酶B吸附至非水相。我们的数据与该反应的一种机制相符，该机制涉及在溶液中协同形成一种解离常数为1.4×10⁻¹⁵M⁴的酶 -（胆盐）₄复合物。游离酶易于吸附至覆盖有胆盐 - 底物的表面，而该复合物则不然。因此，底物水解的“抑制”是由于酶和底物在物理上被分隔开。蛋白质辅因子，即共脂肪酶，通过在界面处为脂肪酶 -（胆盐）₄复合物提供高亲和力结合位点来逆转胆盐的抑制作用。稳态和预稳态动力学数据与形成一种1/1（脂肪酶/共脂肪酶）比例、解离常数为0.4至2.8×10⁻⁹M的复合物相符。脂肪酶吸附至吸附态共脂肪酶的速率似乎受通过未搅拌层的扩散控制，二级速率常数为1.3×10⁶M⁻¹S⁻¹。
