Energy coupling and Hill cycles in enzymatic processes

The enzymatic basis of information processing in the living cell

Analogies are drawn between the computational aspects of information processing and the enzymatic events of cellular metabolism. The origin thereof is linked to the logic-elements involved in the reaction-diffusion processes of the metabolic operation. It is shown how such function entails a 'molecular machine' quality when associated with organized non-equilibrium energy sources in the cell.

Kinetic models of coupling between H+ and Na(+)-translocation and ATP synthesis/hydrolysis by F0F1-ATPases: can a cell utilize both delta mu H+ and delta mu Na+ for ATP synthesis under in vivo conditions using the same enzyme?

Kinetic models of the F0F1-ATPase able to transport H+ or/and Na+ ions are proposed. It is assumed that (i) H+ and Na+ compete for the same binding sites, (ii) ion translocation through F0 is coupled to the rate-limiting step of the F1-catalyzed reaction. The main characteristics of the dependences of ATP synthesis and hydrolysis rates on delta psi, delta pH, and delta pNa are predicted for various versions of the coupling model. The mechanism of the switchover from delta mu H(+)-dependent synthesis to the delta mu Na(+)-dependent one is demonstrated. It is shown that even with a drastic drop in delta mu H+, ATP hydrolysis by the proton mode of catalysis can be effectively inhibited by delta psi and delta pNa. The results obtained strongly support the possibility that the same F0F1-ATPase in bacterial cells can utilize both delta muH+ and delta muNa+ for ATP synthesis under in vivo conditions.

Quantifying heterogeneity: flow cytometry of bacterial cultures

Flow cytometry is a technique which permits the characterisation of individual cells in populations, in terms of distributions in their properties such as DNA content, protein content, viability, enzyme activities and so on. We review the technique, and some of its recent applications to microbiological problems. It is concluded that cellular heterogeneity, in both batch and continuous axenic cultures, is far greater than is normally assumed. This has important implications for the quantitative analysis of microbial processes.