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

[Cr(2gb)(3)]Cl(ZnCl4), [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, CrCl3 and [Co(NH3)(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(ZnCl4) 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 CrCl3 nor [CO(NH3)(6)]Cl-3 inhibited photosynthesis. The 100% inhibition on PS II of [Cr(2gb)(3)]Cl(ZnCl4) is explained in terms of a synergystic effect between the 2gb-chromium(III) coordination compound and the ZnCl42- anion.