Juicing is an excellent way to make nutrients from vegetables more accessible. Juicing traumatizes the vegetable's cell wall enough to release the nutrients but not so much that you're destroying the whole enzymatic protein structure. Whenever you juice a vegetable, you're traumatizing it's cell walls without destroying the enzymes because you're not heating it. In a good quality juicer such a vita mix or a blend tech, the juicing process doesn't seem to destroy the enzymes at all.
Once you've blended the veggies you should drink the juice right away because as soon as it's blended it releases the enzymes from the cellulose, the juice comes into contact with oxygen in the air and the oxidation process begins, chemically changing the juice and neutralizing certain vitamins.