Classic papers on the quantification of respiratory proton ejection

This article looks at two Biochemical Journal papers that are frequently cited as the definitive statement of the quantitative support for Mitchell's chemiosmotic hypothesis in relation to mitochondrial respiration. Both are rich in methodological detail; both contain elaborations of chemiosmotic and biophysical theory. With these two papers, chemiosmotic theory entered the mainstream of bioenergetic thought.

The osmochemistry of electron-transfer complexes

Detailed molecular mechanisms of electron transfer-driven translocation of ions and of the generation of electric fields across biological membranes are beginning to emerge. The ideas inherent in the early formulations of the chemiosmotic hypothesis have provided the framework for this understanding and have also been seminal in promoting many of the experimental approaches which have been successfully used. This article is an attempt to review present understanding of the structures and mechanisms of several osmoenzymes of central importance and to identify and define the underlying features which might be of general relevance to the study of chemiosmotic devices.

Appreciating Key Experiments

SUMMARYGilbert and Mulkay, in their paper ‘Experiments Are the Key’, present responses of scientists to questions about the development of the chemiosmotic hypothesis of energy coupling in oxidative and photophosphorylation, and infer from these responses both the meaninglessness of the concept ‘key experiment’ and the hopelessness of searching for any data as a bedrock for historical analysis. Gilbert and Mulkay's nihilism is, however, rooted in a lack of understanding of the specific scientific issues involved. A closer look at a proposed ‘key experiment’ shows certain obvious characteristics that could be criteria for a ‘key experiment’ moreover, the actual scientific response to that experiment demonstrates its pivotal role in the development of the field. Instead of demonstrating the lack of empirical bases for scientific judgment, Gilbert and Mulkay demonstrate the necessity for identifying the crucial issues and pursuing them, in questioning the scientists as well as in examining other sources.

The relationship between the rate of respiration and the protonmotive force. The role of proton conductivity

It is shown by titrating a suspension of rat liver mitochondria with either ADP or an uncoupler that a specific rate of respiration may not have a unique associated value of the protonmotive force. Alternatively, a specific protonmotive force may not be associated with a unique rate of respiration. It seems that the rate of respiration and the protonmotive force are more sensitive to the agents used for the titrations than to each other. Such observations are not easily explained by the chemiosmotic hypothesis. It is, however, possible provided that the proton conductivities, i.e. the rates of dissipation of the protonmotive force, are considered to be different for each of the agents used to titrate the rate of respiration at the same protonmotive force, or vice versa.