Since PQC is still bound after mild petroleum ether extraction, while PQA is mostly extracted, the results suggest that PQC is on a more specific path to NADP, whereas ferricyanide is on a path that requires PQA. A study
of chlorophyll a fluorescence response in chloroplasts after wet or dry heptane extraction of PQs indicated two sites for PQ function (R. Govindjee et al. 1970). Using the same preparations, Mocetinostat Govindjee et al. (1970) showed that the PI3K inhibitor absorption changes of the reaction center of PS II Chl a-II (now labeled as P680) was not due to Chl a fluorescence artifact. Witt (1971) has summarized spectrophotometric evidence for the two sites involving PQ. Changes in PQ absorption at 265 nm in response to bicarbonate removal also indicates two sites for PQ function between photosystems, but does not identify
which PQs are involved (Siggel et al. 1977; for a review on the role of bicarbonate in the PQ region, see Van Rensen et al. 1999). Extraction of mitochondria by acetone, to remove quinones, showed a specific requirement for coenzyme Q (Ambe and Crane 1960). In chloroplasts, Henninger and Crane (1963) found that acetone extraction removed all of the PQA and PQB, but left 50% of the PQC and PQD; this difference implies a tight binding site for PQC. Acetone extraction also removed 80% of the chlorophyll which makes restoration studies of doubtful significance. Tevini and Lichtenthaler (1970) showed that most of the PQs were in the PS II particles, whereas Vitamin K1 was in the PS I fraction, as measured after removal of the osmiophillic lipid globules. Thus far, the selleck products presence of only PQA, in what Lichtenthaler calls plastoglobuli, has been studied. Lichtenthaler and Peveling (1967) have proposed that the globuli in leucoplasts may act as storage sites for lipoquinones for supply to developing plastids. Under high Histamine H2 receptor light, the globuli continue to enlarge and accumulate PQ which is in the reduced form. Ytterberg et al. (2006) have shown that these globules contain enzymes involved
in PQ synthesis, as well as kinases, which may control PQ synthesis. The hydroquinone is synthesized in globules and is oxidized to quinone when it is transferred to the thylakoid (Lichtenthaler 1977, 2007). In mature leaves from three species, Lichtenthaler and Sprey (1966) found higher amounts of PQ and tocopherylquinone in globules. There was 10–40 times as much PQ in globules than in the chloroplasts. The surprise is that globuli are sites of synthesis instead of being ‘garbage bags’ (Austin et al. 2006). In order to resolve the question of the function of the different PQs, biophysical study of quinone redox changes would be an ideal approach except for the fact that PQA, PQB, and PQC have identical absorption spectra. The other alternative is to find mutants and to discover if the formation of the epoxide derived quinones is under specific genetic control.