Two inhibition targets by [Cr(2gb)(3)](3+) and [Co(2gb)(3)](3+) on redox enzymes of spinach thylakoids.

[Cr(2gb)(3)]Cl(ZnCl(4)), [Cr(2gb)(3)]Cl(3), and [Co(2gb)(3)]Cl(3) were synthesized and characterized. Their chemical structures and the oxidation states of their metal centers remained unchanged in solution. The effects of these compounds, CrCl(3) and [Co(NH(3))(6)]Cl(3), on photosynthesis were investigated. The coordination compounds inhibit ATP synthesis and electron flow (basal, phosphorylating, and uncoupled), behaving as Hill reaction inhibitors. The target for [Cr(2gb)(3)]Cl(ZnCl(4)) is located at the Q(B) level. In contrast, the interaction sites of [Cr(2gb)(3)]Cl(3) and [Co(2gb)(3)]Cl(3) are located in the span from P(680) to Q(A) and at the b(6)f complex. Neither CrCl(3) nor [Co(NH(3))(6)]Cl(3) inhibited photosynthesis. The 100% inhibition on PS II of [Cr(2gb)(3)]Cl(ZnCl(4)) is explained in terms of a synergystic effect between the 2gb-chromium(III) coordination compound and the ZnCl(4)(2)(-) anion.