Which commercial databases are adept in storing biological sequences like Protein/DNA sequence? What are the that have been designed particularly to keep such sequences?

cheers

One sector targetted by Oracle's 10g release was bioinformatics. There's a listing of the appropriate database features around the Oracle site. Find it here. It offers support for BLAST that we think is especially highly relevant to your question.

There's BLASTgres for PostgreSQL, however i don't have any personal expertise by using it.