Mutants ac-115 and ac-141 have one-fifth as much PQ as wild type

Mutants ac-115 and Selleck Wortmannin ac-141 have one-fifth as much PQ as wild type. In these mutants, PS II is blocked; the nature of the remaining PQ is not known. Mutants for the PQ-binding protein in PS II are known and recognized as also acting as the binding site for several herbicides. Which type of PQ can bind at these sites is unknown

(see, e.g., Erickson et al. 1989). Concluding remarks The most important result of my rediscovery of PQ was the identification of a quinone as an electron carrier between Photosystem II and Photosystem I in photosynthesis LY333531 manufacturer (Bohme et al. 1971; see Wydrzynski and Satoh (2005) for the details of PS II; and Golbeck (2006) for the details of PS I). As the hydroquinone can carry protons across the thylakoid membrane, it provides a mechanism for the generation of a proton gradient to drive ATP formation. Ipatasertib Our discovery (or rediscovery) came at a fortunate time since a similar quinone, coenzyme Q, had just been found to function in mitochondrial electron transport. The presence of PQ in green plant chloroplasts focused attention on its role in photosynthesis. Restoration

by PQ of chloroplast electron transport after lipid extraction supported such a role. Further support came from biophysical and genetic analysis. Evidence for quinones in the energy conversion systems of plants, animals, and microbes made the general concept of proton driven energy conversion possible (Wolstenholm and O’Connor 1961). The identification of the PQ binding site as also a site for herbicide action is of practical benefit for herbicide design (Erickson et al. 1989). The discovery of PQB and PQC introduced new problems. Are they waste products from oxidative damage to PQ or do they have other functions? Similar Tryptophan synthase compounds have been related to coenzyme Q in mitochondria (Friis et al. 1967; Sottocasa and Crane 1965) so they may be a product of random oxidative attack on prenyl side chains. PQC is found in amounts similar to Vitamin K1 and α-tocopherol quinone, all of which are found at 1 mol per 100 mol chlorophyll (Table 4). Since that amount is enough for Vitamin K to function in PS I (Biggins and Mathis 1988; Snyder et al. 1991),

PQC and α-TQ are not excluded from a redox role in the chloroplast on the basis of insufficient amount. PQA is found at 10–20 times the concentration of PQC; so, there is enough for other functions (Egger 1965). One of the other functions appears to be redox control as in control of antenna chlorophyll (Allen 2002; Frigerio et al. 2007). Functions of PQ in electron pathways other than photosynthesis have also appeared as in NADH oxidation and carotene synthesis (Norris et al. 1995; Guera et al. 2005). It is also possible to consider if PQC might act as an uncoupler of photophosphorylation. Since coenzyme Q is a cofactor for the uncoupling protein in animal mitochondria, the change in lipophilicity from the hydroxyl group on PQC might change its migration through the membrane, thus affecting proton transfer.

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