If the amount of enzymes is fixed, then as we add substrates, what happens to the # of enzymes?

Question

Will the amount of enzymes be 0 as they will all saturate the amount of substrates? But don't the enzymes get re-used? If so, then nothing should happen to the AMOUNT of enzymes in the vessel

Answer 1

The actual amount of the enzyme(s) does not change .The enzyme is characterized by a kinetic property called the Km which is the concentration of the substrate that will turn the enzyme on to 1/2 its maximal rate of conversion of substrate to the product..after that point it will not convert substrate any faster and the rate plateaus irrespective of the amount of substrate. Since enzymes are biological catalysts they are unchanged from initial structure after the reaction is complete. For instance hexokinase has a Km of ~ 10^5 molar glucose

which means at 10^-5 M glucose, hexokinase is at 1/2 its maximal turnover rate for glucose to glucose -6-phosphate.Glucokinase has a Km of ~ 10^-2 M which means it will not be at 1/2 its maximal velocity until glucose concentrations are 1000 X higher than with hexokinase.

Answer 2

If the amount of enzyme is fixed then it is fixed. As you add more substrate then the active sites of the enzyme become increasingly saturated with the substrate and the reaction rate increases until a point is reached when substrate is in excess and further addition of substrate does not cause any further increase in the rate of reaction.

The enzymes are biological catalysts remember and remain unchanged.