Conclusion
# 1,3-diketones bind in general to the enzyme PBGS of E. coli at the P-site by forming a Schiff base with the e-amino group of the active site lysine probably stabilized in its tautomeric enamine form 2.
# Studying the influence of the relative position of the carboxylate to the diketo system indicates that 1,3-diketones interact with the active site as substrate analogues.
# At this stage of our investigation we can not absolutely exclude the presence of the iminium ion for the inhibitor bound to the enzyme. But we clearly prefer the tautomeric enamine form 2 at the moment.
# 1,3-diketones do not act as analogues of either the intermediate postulated in the Shemin nor in the Jordan II mechanism.
# For the replacement of the carboxylate group by a nitro function in inhibitors recognized at the A-site a considerable increase in inhibition efficiency has been observed.
# The same replacement of the carboxylate group by a nitro function for inhibitors recognized at the P-site the inhibition efficiency decreases.