Effect of low temperatures on cytochrome photoresponse in mouse embryos.

Embryos cryopreservation is a widely used technology for genetic resources storage. Cryopreservation suppresses cell respiration, but very little is known about the changes that occur with mitochondria at low temperatures. We used Raman spectroscopy to investigate photoresponse and redox state of cytochromes in the respiratory electron transport chain (ETC) in early mouse embryos during cooling. Redox state of cytochromes was probed by the intensity of cytochrome resonance Raman lines. Photoinduced reactions of cytochromes were used to study the changes in the rates of redox reactions. It is found that the rate of cytochrome photoresponse detected by Raman spectra abruptly changes when embryos are cooled below -50 °C. Raman mapping revealed that the average intensity of cytochrome Raman peaks at -65 °C is higher than at -40 °C. Cytochrome b reduction was found in embryos frozen below -50 °C when irradiated with 532 nm laser radiation. These effects were observed for cells frozen in aqueous solutions of two different cryoprotectants: glycerol and propylene glycol. Raman spectroscopy of cytochromes reveals the abrupt changes in the ETC work of frozen mouse embryos at temperatures below -50 °C. We suggest that similar phenomena can be found in various cell types.

Cytochrome b 6 f function and localization, phosphorylation state of thylakoid membrane proteins and consequences on cyclic electron flow.

Both the structure and the protein composition of thylakoid membranes have an impact on light harvesting and electron transfer in the photosynthetic chain. Thylakoid membranes form stacks and lamellae where photosystem II and photosystem I localize, respectively. Light-harvesting complexes II can be associated to either PSII or PSI depending on the redox state of the plastoquinone pool, and their distribution is governed by state transitions. Upon state transitions, the thylakoid ultrastructure and lateral distribution of proteins along the membrane are subject to significant rearrangements. In addition, quinone diffusion is limited to membrane microdomains and the cytochrome b 6 f complex localizes either to PSII-containing grana stacks or PSI-containing stroma lamellae. Here, we discuss possible similarities or differences between green algae and C3 plants on the functional consequences of such heterogeneities in the photosynthetic electron transport chain and propose a model in which quinones, accepting electrons either from PSII (linear flow) or NDH/PGR pathways (cyclic flow), represent a crucial control point. Our aim is to give an integrated description of these processes and discuss their potential roles in the balance between linear and cyclic electron flows.

Effect of mutations in the cytochrome b ef loop on the electron-transfer reactions of the Rieske iron-sulfur protein in the cytochrome bc1 complex.

Long-range movement of the Rieske iron-sulfur protein (ISP) between the cytochrome (cyt) b and cyt c1 redox centers plays a key role in electron transfer within the cyt bc1 complex. A series of 21 mutants in the cyt b ef loop of Rhodobacter sphaeroides cyt bc1 were prepared to examine the role of this loop in controlling the capture and release of the ISP from cyt b. Electron transfer in the cyt bc1 complex was studied using a ruthenium dimer to rapidly photo-oxidize cyt c1 within 1 mus and initiate the reaction. The rate constant for electron transfer from the Rieske iron-sulfur center [2Fe2S] to cyt c1 was k1 = 60 000 s-1. Famoxadone binding to the Qo site decreases k1 to 5400 s-1, indicating that a conformational change on the surface of cyt b decreases the rate of release of the ISP from cyt b. The mutation I292A on the surface of the ISP-binding crater decreased k1 to 4400 s-1, while the addition of famoxadone further decreased it to 3000 s-1. The mutation L286A at the tip of the ef loop decreased k1 to 33 000 s-1, but famoxadone binding caused no further decrease, suggesting that this mutation blocked the conformational change induced by famoxadone. Studies of all of the mutants provide further evidence that the ef loop plays an important role in regulating the domain movement of the ISP to facilitate productive electron transfer and prevent short-circuit reactions.

Mitochondrial DNA control region and cytochrome b sequence variation in the genus Mystacoleucus Günther (Pisces: Cyprinidae: Barbinae) from China.

Mitochondrial DNA (mtDNA) hypervariable segment I sequences (HVSI, 471 bp) of the control region and partial cytochrome b sequences (Cytb, 403 bp) were analyzed in three tentative species of the genus Mystacoleucus in China (M. chilopterus, M. marginatus, and M. lepturus). Not more than two mutations were found in both the HVSI and Cytb fragments among the samples from M. chilopterus and M. marginatus. However, M. lepturus differed from each of them by at least 25 mutations in Cytb and 51 mutations in HVSI. Moreover the HVSI sequence variation within M. lepturus was larger than that between M. chilopterus and M. marginatus. Given that M. chilopterus and M. marginatus are very similar in morphology, it is reasonable to consider M. chilopterus and M. marginatus as conspecific. Our results also suggest a recent radiation of M. marginatus from downstream to upstream of the Lancangjiang (Mekong) River.