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 synthesi zed and characterized. Their chemical structures and the oxidation states o f 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 locate d in the span from P-680 to Q(A) and at the b(6)f complex. Neither CrCl3 no r [CO(NH3)(6)]Cl-3 inhibited photosynthesis. The 100% inhibition on PS II o f [Cr(2gb)(3)]Cl(ZnCl4) is explained in terms of a synergystic effect betwe en the 2gb-chromium(III) coordination compound and the ZnCl42- anion.