Common Features of the Active Sites of Enzymes The active site takes up a relatively small part of the total volume of an enzyme Model of myoglobin at high resolution Only the a carbon atoms are shown. The heme group is shown Figure 35-10 in red, and two key Structure of an ATPase fragment histidine residues in derived from hsc70, a cytosolic heat- green. [After R.E. shock protein. ADP (red)is bound in Dickerson. In The he cleft between the two domains Proteins, vol. 2. 2nd (yellow and blue).[Drawn from ed. H. Neurath, ed lats. pdb. K.M. Flaherty, (Academic Press C. DeLuca-Flaherty, and D B. McKay 1964),p.634. Naue346(1990):623.Common Features of the Active Sites of Enzymes