分子与细胞生物学 3 - L2d Reactions and Enzymes (2)

Reactions and Enzymes (2) 

本节内容承接上一部分，主要是对酶的实验室方法讨论（超短预警）不太明白的或者有错误的地方随时来找UP主喔~ 本部分的参考文献Essential Cell Biology, 5th ed. Alberts, et al. 2019. 部分内容来自khanacademy与维基百科.

封面图：https://swh-826d.kxcdn.com/wp-content/uploads/2010/07/substrate-enzyme-complex.jpg（有改动）

2d Lab techniques (Michaelis Menten Kinetics)

Substrate to Product

To get information about an enzyme’s activity:

    1. Mix enzyme & substrate (only varying the [S] in each tube, 这个[ ]表示浓度, [S]即为substrate concentration)

    2. Measure the velocity (V = amount/second, reaction rate)

Determine the relationship between [S] and V

    Low [S]: not all E bind to S, many free E, not much ES complex. V is slow

    As [S] increases: more ES, V is higher

        Until most E is ES, V is even higher, but reach highest V even adding more S, because there will be no free E to bind to. V=Vmax at this point

        As [S] increases, the enzyme becomes more saturated.

Km = [S] needed for V = 1/2 Vmax: how easy is it to saturate the enzyme, how tightly does enzyme bind substrate?

When [S] = Km, the enzyme is half saturated

Vmax is related to how fast ES - EP (step 2, see below)

Km is related to how tightly E binds S (step 1, see below)

        Weak binding, E is less saturated at low [S], Km is large (favors left, S)

        Tight binding, E is easily saturated at low [S], Km is small (favors right, P)

Enzyme Kinetics Experiment Summary:

- Measure: V at various [S]

- Determine:

    Vmax: how fast can the enzyme work when it is saturated with S

    Km: how easy is it to saturate the enzyme

总结：实验中记录反应速率与基质浓度的关系并绘制图像，根据图像判断Vmax以及Km的数值。Vmax即可达到的最大反应速率，体现了酶的最大饱和速率；Km即达到一半Vmax时所需的基质浓度，体现了酶与基质的粘合程度：所需基质浓度越低，则意味着较小的基质浓度就足以让酶达到一半Vmax速率，表明酶更容易与基质粘合。