The enzyme $\beta$-galactosidase is able to catalyse the hydrolysis of four substrates that have similar structures. Each substrate produces a different $K_m$ value. Which substrate does $\beta$-galactosidase have the greatest affinity for?
- Asubstrate 1, $K_m = 4 \times 10^{-3}\ \text{mol dm}^{-3}$
- Bsubstrate 2, $K_m = 1 \times 10^{-3}\ \text{mol dm}^{-3}$
- Csubstrate 3, $K_m = 2 \times 10^{-4}\ \text{mol dm}^{-3}$
- Dsubstrate 4, $K_m = 1 \times 10^{-4}\ \text{mol dm}^{-3}$