Properties of amino acids and protein functional activity - (Feb/06/2012 )

How large impact on protein function could be, if acidic aspartat acid is replaced to basic histidine? How large this impact potentially could be in comparision to change of other chemical properties (for example, when change is between hydrophobe and hydrophile amino acids)?

(Sorry in advance, if someone finds this question to trivial... I am not very familiar with this topic, but I have to get some quick answer.)

This looks suspiciously like homework - if you can tell us what you know, then people will be more ready to help...