Electron microscopic and biochemical evidence that proline‐β‐naphthylamidase is composed of three identical subunits

Electron microscopy of pig intestinal proline-beta-naphthylamidase revealed that the enzyme is composed of 3 subunits, which are assembled in a trifoliolate shape. At pH 4.5 and 4 degrees C, the enzyme dissociates reversibly into active subunits in 4 h. Dissociation also occurs at higher pHs when the enzyme concentration is very low. The activity per mg protein of the native, trimeric enzyme is about 2.5-fold higher than that of the dissociated enzyme.