Chlorophylls and Bacteriochlorophylls: Biochemistry, Biophysics, Functions and Applications. Supplementary Material

I. Substrate specificity of POR Several modified Pchlid derivatives were tested for substrate activity with POR (Griffiths, 1991; Helfrich, 1995; Helfrich et al., 1996; Schoch et al., 1995; Klement et al., 1999). The central Mg can be substituted by Zn while the metal-free Pchlid and the Ni, Co, and Cu complex are inactive. Modifications of the side chains at rings A and B are throughout tolerated without essential loss of activity (Table S1). Starting from Pchlid b, the 7-phenylamino derivative was prepared via the Schiff base. This turned out to be a good substrate indicating free space around ring B when the substrate is bound to the active center of POR. By contrast, only very limited space around ring E is apparently left after substrate binding: only compounds with the natural 13(R)-configuration (e.g. Pchlid a ) are substrates while the 13 (S)compounds (Pchlid a’) are not, and the activity is almost lost by exchange of the natural 13-methoxy compound by the 13-ethoxy compound (Table S2). The activity is completely lost, in contrast to the properties of Chl synthase (see section on Chl synthase), by exchange of the proton at C-13 against a hydroxyor methoxy-group.