When k2 is very small ( k2 << k1 ) that is:
slow, infrequent E + S <---> ES ----------------------> Pthen: which is equal to the dissociation constant Kd for the equilibrium:
Kd is a measure of how tightly the enzyme binds to the substrate (Note the similarity to a Ka for dissociation of an acid). Therefore, Km is an approximate measure of the affinity of the substrate for the enzyme.
Vmax and Km are the two parameters which define the kinetic behavior of an enzyme as a function of [S].
"Vmax is a measure of how fast the enzyme can go at full speed."
Vmax is a rate of reaction. It will have units of:
"Km is a measure of roughly how much substrate is required to get to full speed. If [S] >> Km then Vo will be close to Vmax."
Km is a concentration. It will have units of: