This enzyme (penicillin acylase) is made of two subunits (dark and light blue). Bound to the active site is penicillin (green) and a calcium ion (red).
Reset View of Penicillin Acylase from E. coli.

What sort of secondary structure is present in this enzyme? Are there any disulfide bonds?

No, this protein lacks any cysteines and so there are no disulfide bonds holding the two subunits together.

Isolate the smaller subunit (dark blue) or the larger one (light blue) . Which subunit binds the calcium ion? How is the active site for penicillin formed? You might want to rotate the structure and zoom in some.

Here is the answer:
Calcium binding by four negatively charged acidic residues (red) . Three are from the larger subunit (light blue) and one is from the small subunit (dark blue).

Penicillin's binding site is formed almost exclusively by the large subunit .


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