The last example is a funny rodent because its sequence is closer to all kinds
of horses than to other rodents. So either this sequence has not been determined
in any rodent yet, or something is rotten, or this will be a goldmine for phylogeny
and taxonomy researchers. The active site residues are determined the same way as
in the previous example.
There are also BLAST hits to seamamals and African animals (including one African rodent). Please remember that a few hundred million years ago Africa and South America were one continent and they separated only after a very big sea came into existence 'between' them.
In de database sequence *MYG_EQUBU (first or second hit, score exactly as high as HORSE...) the histidines are 65 and 94. In the funny rodent they are 61 and 90