SB C/P #33c

[lostnconfused]

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The question asks for the variant with the lowest catalytic efficiency. My question is why, per the AAMC explanation, do we need to look at the ratio of kcat/Km? I arrived at the answer by looking at just Km or kcat. However the explanation said to look at the ratio. I notice the AAMC does this a lot - comparing ratios instead of one constant. Can somebody please clarify?

Thank you.

 

[aldol16]

Catalytic efficiency or specificity is defined as the ratio of kcat/Km.

 

[sugar6594]

Catalytic efficiency depends on (1) the slowest step of the reaction (normally ES → P) and (2) how well the enzyme binds the substrate.

(1) would be your kcat
(2) would be your Km

To determine efficiency, always use kcat/km

Neither one by itself could indicate the catalytic efficiency.

If you did end up looking at one or the other to determine efficiency, I am not sure how you would arrive at (D) by only looking at the kcat because (C) has a lower kcat.