Gnaiger 1980 Thermochim Acta
|Gnaiger E (1980) Das kalorische Äquivalent des ATP-Umsatzes im aeroben und anoxischen Metabolismus. Thermochim Acta 40:195-223.|
Abstract: The turnover rate of ATP is one of the most general bioenergetic quantities independent of the type of metabolism (aerobic or fermentative) and of the coupling efficiency (P/2e− ratio etc.). It links the various processes of catabolism and anabolism as an expression of the “biochemical speed of rotation”. Similarly, the rate of heat production is considered an unspecific measure of metabolic rate applicable under aerobic and anoxic conditions. The interpretation of biocalorimetric data in terms of ATP-turnover, however, requires a detailed thermochemical analysis of the biochemical pathways, i.e., of their stoichiometries and reaction enthalpies under physiological conditions, and of the molar ATP equivalent of any particular pathway. Such analyses are presented for aerobic and fermentative catabolism characteristic of organisms ranging from bacteria to higher animals including man.
The caloric equivalent of disspative ATP-turnover under non-growing conditions, Cd∞ATP varies from 76 to 83 kJ·mol−1 ATP in aerobic metabolism, assuming a P/O-ratio of 3. In contrast to the uniform catabolic pathway in aerobic organisms a variety of fermentative reactions exists which differ with respect to reaction enthalpy and efficiency of phosphorylation. Under anoxia the caloric equivalent of ATP turnover is reduced under most conditions relative to the aerobic Cd∞ATP. This reduction amounts to up to 30 % in lactate and ethanol fermentation of glucose and from 30 to 50 % in propionate and acetate fermentation. Hence anoxic rates of heat production may be significantly less than the aerobic rate without a corresponding reduction of metabolic rate expressed as ATP-turnover. Direct comparison of rates of heat dissipation observed under different physiological conditions may lead to erroneous conclusions regarding the metabolic activity of organisms.
Organisms growingaerobically on glucose may theoretically conserve up to, but rather less than 25 % of the catabolic reaction enthalpy in net biosynthesis. Uncertainties of energy balance calculations, however, stem primarily from the variability of physiological "side reactions", such as enthalpies of neutralization and complexation. Their significance in the estimation of caloric efficiencies of metabolism is discussed on the basis of the present state of biological thermochemistry. An experimental example with aquatic invertebrates illustrates the unique potential of the direct calorimetric method in quantitative bioenergetics, while it also points to some specific problems associated with the biochemical interpretation of thermometric measurements.
• Bioblast editor: Gnaiger E • O2k-Network Lab: AT Innsbruck Oroboros
Labels: MiParea: Respiration
Stress:Hypoxia Organism: Annelids
Preparation: Intact organism
Regulation: ATP production, Coupling efficiency;uncoupling, pH