Synechococcus sp. PCC 7002 CpcB lyase null mutations alter phycocyanin chromophore function and, consequently, affect the redistribution of excitation energy via the light state transition /

Phycobilisomes are the major light harvesting complexes for cyanobacteria and phycocyanin is the primary phycobiliprotein of the phycobilisome rod. The phycocyanobilin lyases responsible for chromophorylating the phycocyanin p subunit (CpcB) have been recently identified in the cyanobacterium Synechococcus sp. PCC 7002. Surprisingly, mutants missing the CpcB lyases were nevertheless capable of producing pigmented phycocyanin. 10K absorbance measurements revealed that the energy states of the p phycocyanin chromophores were only subtly shifted; however, 77K steady state fluorescence emission spectroscopy showed excitation energy transfer involving the targeted chromophores to be highly disrupted. Such evidence suggests that phycobilin orientation within the binding domain is specifically modified. We hypothesized that alternate, less specific lyases are able to act on the p binding sites. A phycocyanin linker-polypeptide deficient mutant was similarly characterized. The light state transition, a short term adaptation of the photosynthetic light harvesting apparatus resulting in the redistribution of excitation energy among the photo systems, was shown to be dominated by the reallocation of phycocyanin-absorbed excitation energy. Treatment with a high M phosphate buffer effectively prevented the redistribution of both chlorophyll a- and phycobilisome- absorbed excitation energy, suggesting that the two effects are not strictly independent. The mutant strains required a larger redistribution of excitation energy between light states, perhaps to compensate for their loss in phycobilisome antenna function.

Effect of citrate on the redox properties of cytochrome C and its kinetic and binding behaviour with cytochrome oxidase /

Increasing citrate concentration, at constant ionic strength (30 mM) decreases the rate of cytochrome ~ reduction by ascorbate. This effect is also seen at both high (600 mM) and low (19 mM) ionic strengths, and the Kapp for citrate increases with increasing ionic strength. Citrate binds d both ferri -and ferrocytochrome ~, but with a lower affinity for the latter form (Kox . .red d = 2 mM, Kd = 8 mM) as shown by an equilibrium assay with N,N,N',N', Tetramethyl E- phenylenediamine. The reaction of ferricytochrome ~with cyanide is also altered in the presence of citrate: citrate increases the K~PP for cyanide. Column chromatography of cytochrome ~-cytochrome oxidase mixtures shows citrate increases the dissociation constant of the complex. These results are confirmed in kinetic assays for the "loose"site (Km = 20 pM) only. The effect of increasing citrate observable at the "tight" site (Km = 0.25 pM) is on the turnover number and not on the K . These results suggest a mechanism m where anion binding to cytochrome £ at the tight site affects the equilibrium between two forms of cytochrome c bound cytochrome oxidase: an active and an inactive one.

Chronic versus acute ingestion of sodium citrate: a randomized placebo controlled cross-over trial for swimming 200 metres in well-trained swimmers age 13-17

A double-blinded, placebo controlled, cross-over design was used to investigate sodium citrate dihydrate (Na-CIT) supplementation improve 200m swimming performance. Ten well-trained, male swimmers (14.9 ± 0.4y; 63.5 ± 4kg) performed four 200m time trials: acute (ACU) supplementation (0.5g/kg), acute placebo (PLC-A), chronic (CHR) (0.1g/kg for 3 days and 0.3g/kg on the 4th day pre-trial), and chronic placebo (PLC-C). Na-CIT was administered 120min pre-trial in solution with 500mL of flavored water; placebo was flavored water. Blood lactate, base excess (BE), bicarbonate, pH, and PCO2 were analyzed at basal, 100min post-ingestion, and 3min post-trial via finger prick. Time, lactate, and rate of perceived exertion were not different between trials. BE and bicarbonate were significantly higher for the ACU and CHR trials compared to placebo. “Responders” improved by 1.03% (P=0.043) and attained significantly higher post-trial lactate concentrations in the ACU versus PLC-A trials and compared to non-responders in the ACU and CHR trials.