Characterization of a prolyl endopeptidase from spinach thylakoids

Abstract

A prolyl endopeptidase (PEPase, EC 3.4.21.26) that specifically cleaves the 18‐kDa protein of photosystem II was extracted from photosystem II membranes with 1 M NaCl. Proteolytic activity measured with artificial substrates was less than a quarter of that with the protein. Studies on inhibition of the proteolysis by an artificial substrate suggested that the protease recognizes the scissile prolyl bond. The protease was inhibited by CuCl₂, but not by diisopropyl fluorophosphate or p‐chloromercuriphenylsulfonic acid. These findings suggest that the protease represents a new class of PEPase. The specificity of the enzyme is discussed in relation to the structure of the 18‐kDa protein.