Macromolecular hemochromes: the system ferroprotoporphyrin IX-polylysine in aqueous medium.

Light-absorption spectra of complexes between reduced iron-protoporphyrin IX (2 X 10-S M) and various polylysine samples (up to 2 X 1OW residue molar) were measured in the range 380-630 rnp in deaerated aqueous solutions of pH 12 and at 27”. The absorption spectra obtained were very similar to well-known ferrohemochrome spectra of proteins or of complexes of protoheme with low-molecular-weight nitrogenous bases at high concentrations. In contrast to analogous complexes of trivalent, iron, there was no fundamental spectral difference, under opt,imum conditions, betweeu complexes involving either polya,L-lysine or poly-a,nL-lysine. A 0.04 M L-lysine monomer did not, produce a ferrohemochrome, but 0.01 M n-butylamine formed it, to a large extent. The hemochrome band at 558 rnp of the synt,het.ic complex ferroprotoporphyrin IX-poly-CY,L-lysine had its maximum ext’inction at pH 12.1. In the abseuce of air and at, room temperature, reduction of the trivalent iron-protoporphyrin IX in the presence of poly-a,~-lysine by either excess sodium ascorbate or dithionite led to the same spectral data. The synthetic macromolecular ferrohemochromes were autoxidizable. The integrat,ed absorption of the various light-absorption bands was significantly higher for synthetic complexes involving higher molecular weight poly-a,L-lysine (up = 700) than for those of lower molecular weight (DP = 70).