It is achievable for the same enzyme to catalyze reverse reactions for the reason that the direction of a reversible reaction is determined by the concentrations of reactants and products. In pulmonary circulation, the low CO2 concentration supports the making of CO2 and H2O.
For the formation of nitrogen dioxide, the reactants used are nitrogen monoxide and oxygen gas. 2 moles of nitrogen monoxide gas react with 1 mole of oxygen gas to produce 2 moles of nitrogen dioxide gas.