Myoglobin

Myoglobin  is a small protein having mass of 17.8 kDa made of 153 amino acids  in a single  polypeptide  chain.  It was  the 1st  protein  to have  its 3- dimensional  structure  determined  by the X-ray crystallography  by the scientist John  Kendrew  in the year 1957.  Myoglobin  is a characteristic  globular  protein  in that it is a highly  folded  compact  structure  with  most  of  the  hydrophobic   amino  acid residues buried in the interior and many of the polar residues on the surface. X- ray crystallography   revealed that the single polypeptide chain of myoglobin consists entirely of   α-helical secondary structure. In fact there are eight α-helices (labeled A–H) in myoglobin as shown in figure given below.Within a hydrophobic Crevice formed by the folding of the polypeptide chain is the heme prosthetic group as shown in figure a. This nonpolypeptide unit is noncovalently bound to myoglobin and is very much essential for the biological activity of the protein (that is the binding of O₂).