coli, yeast and humans support [54] that indirect protein interactions between related enzymes achieve metabolic channeling. Interestingly, protein complexes include nonenzymatic mediator proteins, sometimes related to signal transduction, to form channeling modules. In E. coli reactions, possessing such interactions show higher flux. Channeling could lead to more cross-talk. However, Pérez-Bercoff et al. [54] find that scaffolding proteins limit this,

keeping protein complexes in separate places. Furthermore, there are interesting differences in the channeling of Inhibitors,research,lifescience,medical glucose towards gluconate and other catabolic end-products like pyruvate and acetate, with respect to phosphate status for different Pseudomonas strains (Pseudomonas aeruginosa versus P. fluorescens) [55]. Enzyme activities including glucose dehydrogenase, glucose-6-phosphate dehydrogenase and pyruvate carboxylase change in a coordinated fashion in response to changes in growth, glucose utilization or gluconic

Inhibitors,research,lifescience,medical acid secretion. This includes a shift of glucose towards a direct oxidative pathway under phosphate deficiency which may perhaps also be implied in the different abilities of the two strains to produce gluconic acid. Comparison of enzyme–enzyme interactions in metabolic networks of E. coli and S. cerevisiae shows evidence for direct metabolic channeling [56]. Enzyme–enzyme interactions occur more often for pathway Inhibitors,research,lifescience,medical neighbors with at least one shared metabolite. Non-neighbouring interactions are often regulatory. Molecular crowding: Crowding effects do change prokaryotic enzymes, metabolism and promote protein complexes in prokaryotes. Where metabolic channeling is a specific 2MeOE2 effect between metabolic proteins (enzymes

and protein mediators) in a complex, molecular crowding is instead a more Inhibitors,research,lifescience,medical general, unspecific effect by the combined variety of biomolecules (Figure 3b), including nucleic acids, proteins, polysaccharides, as well as other soluble and insoluble components and metabolites (total concentration 400 g/L). The reason for the crowding effect is thus that Inhibitors,research,lifescience,medical together these biomolecules occupy a significant proportion (20–40%) of the total cellular volume in cytoplasm and nucleus, respectively [57]. Biophysical effects from crowding differ thus in different compartments of cells. Many nuclear processes such as gene transcription, hnRNA splicing and DNA replication, Tryptophan synthase assemble large protein–nucleic acid complexes. Macromolecular crowding provides a cooperative momentum for these [58], boosting functionally important nuclear activities. In cell membranes, membrane proteins occupy approximately 30% of the total surface area leading to crowding effects on the surface as well as unique effects for the even more movement restricted integral membrane [58]. Thus Wang et al. [59] directly monitored the effect of strong crowding on pressure-induced reduction of unfolding of a protein (staphylococcal nuclease) by tryptophan fluorescence.