Protein sequencing and amino acids

[rikajaj]

If every protein is composed of a specific sequence of amino acids, how is it that the protein myoglobin in humans has a different sequence than the protein myoglobin in horses?

[mith]

Because proteins aren't named according to their sequences?

[MrMistery]

well actually they do not have the same name. you need to look up what protein families and superfamilies are. no 2 proteins will bear the same name and still have different amino acid sequences.
So, even if we call hemoglobin the same regardless which one of the 2 million alleles a particular person has, the correct way to call it would be something like Human_hemoglobin for the one designed as the "normal one" and Human_hemoglobin61Y for the one with a tyrosine at 61. Now i just made up that naming system, but the official one is similar in principle.
It really depends if you are a biology student, a physiologist, a doctor or a biochemist. they each refer to them differently.