Which of the following is correct concerning the km of an enzyme?
(a) it depends on the dissociation constant for the product of the reaction.
(b) it defines the vmax of the enzyme-catalyzed reaction.
(c) it is a measure of the number of substrate molecules converted to product in a specific unit of time.
(d) it is the substrate concentration at which the velocity of the reaction is equal to 1/2 vmax.
(e) it is measured in units of moles per minute.