PROSTAGLANDIN-H SYNTHASE - INACTIVATION OF THE ENZYME IN THE COURSE OF CATALYSIS IS ACCOMPANIED BY FAST AND DRAMATIC CHANGES IN PROTEIN-STRUCTURE

Prostaglandin H synthase (PGHS) as apo-PGHS, holo-PGHS, and holo-PGHS, inactivated in the course of catalysis was studied using chemical mod ification with diethyl pyrocarbonate (DEPC). The exhausted reaction wi th DEPC corresponded to the modification of 7 histidine residues in ap o-PGHS and 4 in holo-PGHS. All 18 histidine residues became accessible for modification with DEPC in the enzyme, inactivated in the course o f catalysis. The velocities of tryptic cleavage of all the three forms into two fragments were fairly different but independent of modificat ion. Based on the results we hypothesize fast and dramatic changes in the protein structure in the course of the substrate conversion.