Light, time and micro-organisms
3 > pts > -3
Milliseconds to kiloseconds. The third time domain
The proton motive force, a transmembrane electrochemical gradient of hydrogen ion concentration, may drive any one of a number of endergonic reactions, chief among which is synthesis of ATP. The means by which ATP synthesis results from movement of protons back across the coupling membrane can be inferred clearly from the structure of the extrinsic F1-ATPase of bovine heart mitochondria.
Adaptation.Adaptations begin in third time domain. It is possible to magnify the part of the pts scale that corresponds to the boundary between domains three and four.
If physiology is fine-tuning the structure, function, and interactions of pre-existing proteins, a clear example is post-translational, covalent modification. The most versatile and widely-deployed case appears to be protein phosphorylation. In chloroplasts, protein phosphorylation has an accepted, central role in the mechanism by which the light-harvesting complex II becomes redistributed between photosystem I and photosystem II (Allen, 1992). Protein phosphorylation is implicated in physiological control of excitation energy transfer in cyanobacteria and purple photosynthetic bacteria, too, despite the absence, in the latter, of the problem of redistribution of light-harvesting function between reaction centres of two different kinds. In chloroplasts, it is now known that phosphorylation of a sub-population of light-harvesting complex II polypeptides at the periphery of photosystem II induces a structural change at their amino-terminus (Nilsson et al., 1997).
|The Nobel Prize in Chemistry, 1997|
|Yoshida: Direct observation of the rotation of F1-ATPase|
|Protein kinase resource|
|John F. Allen: Mitochondrion and the "vicious circle" theory of ageing|