Profile 2, update separate database on submit?
Every module which exposes hooks are documented in module *.api.php file. In your case it's just hook_profile2_update .

/**
* Respond to a profile being updated.
*
* This hook is invoked after the profile has been updated in the database.
*
* @param $profile
*   The $profile that is being updated.
*
* @see hook_entity_update()
*/
function hook_profile2_update($profile) {
  db_update('mytable')
    -&gt;fields(array('extra' =&gt; $profile-&gt;extra))
    -&gt;condition('pid', $profile-&gt;pid)
    -&gt;execute();
}


Refer http://cgit.drupalcode.org/profile2/tree/profile2.api.php for more details.