Predicting in vivo oxygen consumption rate from ETS activity and bisubstrate enzyme kinetics in cultured marine zooplankton

Oxygen consumption rates ( R_O_2 ) in the rotifer Brachionus plicatilis and the mysid Leptomysis lingvura during both well-fed conditions and starvation have been modeled using the electron transport system (ETS) activity, bisubstrate kinetics and intracellular concentration of substrates. Furthermore, the influence of the food quality on the respiratory metabolism and metabolite levels has been explored. The highest values of most of the variables both in rotifers and mysids were mainly found on organisms grown on the lipid-rich diet, although no differences were determined between treatments in the response to starvation. Time courses of the R_O_2 and the concentration of pyridine and adenine nucleotides evidenced a sharp decrease during food shortage and a fast recovery with food restoration, whereas the potential respiration ( Φ ) remained fairly constant. In general, the modeled R_O_2 ( V_O_2 ) predicted with a high degree of success in the in vivo R_O_2 , even though it yielded relatively lower values. Nonetheless, the correlation of the measured R_O_2 with V_O_2 during starvation was much better than with the R_O_2 estimated from ETS measurements and a fixed R_O_2 / Φ ratio. Finally, the observed relationship between the measured R_O_2 and the adenine nucleotide ADP suggests that the contribution of this nucleotide should be included in future applications of this model.