How do fish deal with deep sea pressure?

[d]

What are some adaptations of deep sea fish to buoyancy and pressure? what are ( if any) the special enzymes, protein or lipid structures and functions?

[incitatus]

For specifics you need to see specific species. Enzymatically there is not much need for change, but bony structures are subject to pressure induced oxygen lysis and so cartilaginous structures are favoured. Buoyancy is dealt with using oil chambers rather than swim bladders, but aside from that mostly the structures are the same. None of the adaptations is unknown in surface species. The most interesting adaptations tend to be the light organs and toxins ... which are of uncertain biosynthetic origin.
Some deep sea species are very strange, the so called "Black Smoker Lifeforms" as these rely on sulfur as a basic energy source rather than oxygen. These are not what most people have in mind, however, when they talk of deep sea fish.