Question

With respect to Vmax (biochemistry), specify whether changes in substrate or enzyme concentration will lead to changes and explain your reasoning using a biochemical description of enzymes/formulas.

Answer 1

Ans. #1. Change in [S]: Change in [S] does not affect the Vmax. Vmax is defined as “maximum reaction velocity attainable when enzyme is saturated with substrate”.

That is, the term Vmax is specific to the reaction velocity when [S] is sufficient enough to saturate all enzyme molecules. Increasing the [S] above saturation level does not affect Vmax or does not increases Vo.

Therefore, Vmax remains unaffected of [S].

However, lowering the [S] also lowers the instant reaction velocity, Vo. When [S] is lower than saturation level, substrate molecules are not available for some enzyme molecules. So, less enzymes are actually converting the substrate into product. Or, less product is formed per unit time.

Therefore, though change in [S] does not affect Vmax, lowering [S] lowers the Vo.

#2. Consider an example. There are 100 enzyme molecules in a reaction mixture, and each enzyme forms one product per unit time, and [S] is at saturating level. So, overall, there would be 100 products formed per unit time. Therefore, Vmax in this case would be 100 per unit time.

When there is only 50 enzyme molecules in reaction, only 50 product molecules would be formed even if [S] is saturating. That is, lowering number of enzyme molecules also lowers the rate of product formation. In this case Vmax is lowered to 50 per unit time.

Similarly increasing the [E] also increase the Vmax, given [S] is at saturating level.

# Therefore, Vmax is directly proportional to [E] because it is the each individual enzyme molecule that actually converts substrate into products.

So, if you increase [E], Vmax would increase proportionally.

If you decrease [E], Vmax would decrease proportionally.