This paper reports the results of research on the interaction between the cytochrome f of the active cytochrome bf complex (incubated with Cd-, Zn-, and Ag-substituted plastocyanins) and Cu-plastocyanin. The presented studies show, that the metal derivatives of plastocyanin can have an influence on the photosynthetic electron transfer path: cytochrome b6fcomplex - photosystem I. The metal-substituted plastocyanins occupy the plastocyanin electron transfer site of the cytochromef The stopped-flow measurements show, that although the metal derivatives of plastocyanin do not influence the rate of cyt f - Pc electron transfer, creation of the non-electron-transfer complexes characterised by a strong binding between the cyt f and substituted plastocyanins and their slow release, dependent on the redox state of the substituted metal, results in the decrease of a turnover of the cytochrome complex.