Why are enzyme-catalysed reactions slower at lower substrate concentration?

Question

Suppose I'm using 200 nmoles of enzyme and 2 mmoles of substrate. The enzyme should be saturated but if I use 50 mmoles of substrate, the reaction will be faster. Why?I just can't get it! Even at lower concentration of substrate the enzyme is saturated (all enzyme molecules are engaged in the reaction) but still the reaction rate is lower.

Answer 1

Chemical reactions rely on collisions. Fewer substrate molecules mean fewer collisions between the enzyme and the substrate.