Energy metabolism metabolic zoning

Periportal zone/Zone 1 Glucose release Oxidative energy metabolism Amino acid utilization Protection against oxidants Bile acid uptake and excretion Bilirubin excretion... 

Diffusion-mediated release of root exudates is likely to be affected by root zone temperature due to temperature-dependent changes in the speed of diffusion processes and modifications of membrane permeability (259,260). This might explain the stimulation of root exudation in tomato and clover at high temperatures, reported by Rovira (261), and also the increase in exudation of. sugars and amino acids in maize, cucumber, and strawberry exposed to low-temperature treatments (5-10°C), which was mainly attributed to a disturbance in membrane permeability (259,262). A decrease of exudation rates at low temperatures may be predicted for exudation processes that depend on metabolic energy. This assumption is supported by the continuous decrease of phytosiderophore release in Fe-deficient barley by decreasing the temperature from 30 to 5°C (67). 

TAT liposomes remain intact within one hour of translocation and slowly migrate through the cell, bypassing the endocytic pathway, to the perinuclear zone where they disintegrate (95). The mechanism utilized by TAT to migrate across the membrane was thought to be energy independent because it operates at similar rates at both 4°C and 37°C (95,96). Cell entry by TAT is also unhindered by metabolic inhibitors such as sodium azide or iodoacetamide (97). Peptides constructed of both the d and l amino acids of Antp can be detected intracellularly, the inference of which is that no specific receptor was required because both isomers had equal potential (98,99). 

Environmental conditions related to rock surface exposure have profound effects on biofilm development, as metabolic activity and growth are directly connected to the availability of water, energy sources and nutrients, as well as to conditions of temperature and irradiation. Another important factor for establishment of subaerial biofilms is the resistance of the supporting substrate to environmentally and biologically influenced disintegration and dissolution (wear-down). Rapidly weathering rock surfaces (e.g. porous sandstone in an intertidal coastal zone) show little or... 

Competition for fermentation products produces a succession of dominant metabolic pathways as distance from the source of electron donors and acceptors increases. Aerobic metabolism dominates the surface of sediments, and methanogenesis the deeper depths, as suggested by their free energy yield (Table 1). There is often very little overlap between each zone, suggesting nearly complete exclusion of one group by another. The same pattern is observed with distance from the surface of a root or burrow, or with distance downstream from an organic pollutant source in rivers and aquifers. 

Reductive metabolism captures free energy ultimately produced by the fission of uranium, thorium, and potassium-40 in the earth s mantle, but makes no use of the richer free energy stress from solar fusion reactions, other than exploiting liquid water as a solvent in the habitable zone. Photosynthesis captures this independent fusion energy source, but appears to have become accessible only with the molecular complexity of modem cells. It therefore evolved to be self-supporting by artificially... 

---