INHIBITION BY PENEM OF PROCESSING PEPTIDASES FROM CYANOBACTERIA AND CHLOROPLAST THYLAKOIDS

Proteins targeted to the thylakoid lumen of plants and cyanobacteria a nd the periplasmic space of cyanobacteria are synthesised with N-termi nal presequences which are removed following translocation across the membrane, These presequences are thought to direct translocation of th e preprotein by a sec-type pathway. Detergent extracts of cyanobacteri al and chloroplast membranes contain enzymes which are capable of proc essing precursors to the mature size. We show that the processing of a range of precursors by both cyanobacterial and chloroplast enzymes is inhibited by the penem SB216357. This is the first report of an inhib itor of these enzymes and indicates that they are type 1 signal peptid ases.