Effects of heterocyclic and tertiary permeant amines on the electron transfer in thylakoid membranes

The effect of low concentrations (up to 50 μM) of lipophilic permeant amines on the electron transfer in thylakoid membranes of pea chloroplasts has been investigated. In the presence of heterocyclic amines (9-aminoacridine and neutral red), the electron transfer, initiated from H₂O to PS I acceptors, has been shown to be inhibited to a level amounting to less than 50% of control, this taking place for both the basal (at alkaline pH) and the gramicidin-uncoupled transport (at pH 6.5–8.5). Under the same conditions, tertiary amines (dibucaine, tetracaine) cause only a 10–15% inhibition of transport. With all the amines, the rate of electron transport from H₂O to DCBQ, PS II acceptor is decreased to 80–90% of control at pH above 8.0, but this effect is completely removed when pH is lowered to 7.7–6.5. In the region of PS I, all the amines accelerate the basal transport, but do not influence the uncoupled electron transfer. A conclusion has been drawn that, parallel with uncoupling, heterocyclic and tertiary amines also cause an inhibition of PS II, appearing at alkaline pH values. Additionally, heterocyclic amines seem to brake electron flow at the level of plastoquinone reduction. This revised version was published online in June 2006 with corrections to the Cover Date.