Infrared spectroscopy was used to evaluate the effect of non-iron porp
hyrins (protoporphyrin IX and haematoporphyrin) on haematin polymerisa
tion to beta-haematin at acidic pH. Both molecules effectively inhibit
ed the reaction, with haematoporphyrin 6 times as active as protoporph
yrin IX, We postulated that the interaction between the pi electron sy
stem of porphyrin rings leads to the formation of pi-pi adducts, which
inhibit polymer elongation in the same way as antimalarial drugs (e.g
., chloroquine); the presence of hydroxyl groups able to bind haem iro
n enhances activity. (C) 1997 Federation of European Biochemical Socie
ties.