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DELICATE BALANCE. "The energy wasteful reactions are a particular problem for photosynthetic reaction centres because the photochemistry gives such high energy intermediates. This problem is mainly dealt with through kinetic control: i.e. the forward reactions are faster than the back reactions. This is achieved by having cofactors appropriately spaced within the protein to allow rapid vectorial electron transfer across the membrane, separating the positive and negative charges from each other." https://lnkd.in/dxpcWx8 View in LinkedIn

"EMBRYONIC and neonatal mice can regenerate their digit tips if they are amputated through the distal phalanx, and similar digit tip regeneration occurs in humans." http://onlinelibrary.wiley.com/doi/10.1111/j.1440-169X.2007.00973.x/full View in LinkedIn

ANCIENT WORK-AROUNDS. "The energy-converting redox enzymes perform productive reactions efficiently despite the involvement of high energy intermediates in their catalytic cycles. This is achieved by kinetic control: with forward reactions being faster than competing, energy-wasteful reactions. This requires appropriate cofactor spacing, driving forces and reorganizational energies." https://lnkd.in/dxpcWx8 View in LinkedIn

PREVIOUSLY EFFICIENT. "The energy-converting enzymes evolved from ancestral enzymes that functioned in conditions of low O2 concentration or anaerobicity. These ancestral proteins did not have to deal with the inevitable side-reactions (leaks) that occur when O2 is present." https://lnkd.in/dxpcWx8 View in LinkedIn

REMODELED VESTIGIAL MOLECULE. "All known photosynthetic reaction centres share the common structural feature of pseudo-C2 symmetry both at the level of the protein backbone and of the arrangement of the redox cofactors. This reflects their evolution from a common ancestral reaction centre which was made up of a homodimer of core protein subunits." https://lnkd.in/dxpcWx8 View in LinkedIn

FUTILE CYCLE UTILITY. "When the cytochrome b 559 is already oxidized, the carotenoid cation can be reduced by chlorophyll, most likely ChlZD2, which is calculated to have a uniquely low potential. This branch of the futile cycle may serve as a trap for the cation and as a fluorescence quencher that will protect against over excitation of PSII." https://lnkd.in/dxpcWx8 View in LinkedIn

MORE WRENCHING THE SYSTEM. "In order to work so much more efficiently, some kind of redox switch seems to be required. It was suggested recently that this could involve a perturbation of the relative redox potentials of the core chlorophylls so that the chlorophyll cation may be distributed onto ChlD2, i.e. closer to the carotenoid." https://lnkd.in/dxpcWx8 View in LinkedIn

VARIATIONS ON A FIX THEME. "This inefficient Cyt b 559-mediated cycle has been proposed to protect against oxidative damage caused by inline image or by Car +. In marine plankton a much more efficient futile cycle exists under high light. This may represent a souped-up version of the Cyt b 559 cycle described here." https://lnkd.in/dxpcWx8 View in LinkedIn

CHEMISTRY AND POSITION FIXES. "The very high potentials involved in water photolysis can result in the adventitious oxidation of nearby organic species in and around the PSII reaction centre. To work as quenchers of chlorophyll triplets, carotenoids need to be very close, van der Waals contact is typical. Thus carotenoids cannot protect the core chlorophylls in PSII and indeed the crystal structure verified this prediction." (PSII = photosystem II) https://lnkd.in/dxpcWx8 View in LinkedIn

OXIDATION PROTECTION. "In PSII, given the extreme oxidising chemistry associated with water oxidation and generation of O2, there are other protective mechanisms that appear to be there to prevent over-oxidation of the cofactors and groups in their environment (These too may have secondary reactions associated with O2 and its derivatives." https://lnkd.in/dxpcWx8 View in LinkedIn