01-22-2012, 02:07 PM
Vmax is the maximum velocity or rate at which the enzyme catalyzed a reaction...and it depends only on Number of the enzymes not *substrate concentrations,so increased or decreased* [substrates] will not change the amount of Vmax
....so in this case at the new concentration (5*10^-4) ,enzyme A works at its Vmax,which is 20 mmol/min.