Which statements about the Michaelis–Menten constant (Km) of an enzyme are correct? 1 At the Km value, half the active sites of the enzyme should be occupied by the substrate. 2 Km represents the substrate concentration at which the enzyme is working at half its maximum rate. 3 The lower the Km value, the lower the affinity of the enzyme to its substrate. 4 When an enzyme has a high Km value, the enzyme-catalysed reaction will proceed very slowly to its maximum rate.