Modeling physiological processes in plankton on enzyme kinetic principles

Abstract

Many ecologically important chemical transformations in the ocean are controlled by biochemical enzyme\nreactions in plankton. Nitrogenase regulates the transformation of N2 to ammonium in some cyanobacteria and serves as the\nentryway for N2 into the ocean biosphere. Nitrate reductase controls the reduction of NO3 to NO2 and hence new production\nin phytoplankton. The respiratory electron transfer system in all organisms links the carbon oxidation reactions of intermediary\nmetabolism with the reduction of oxygen in respiration. Rubisco controls the fixation of CO2 into organic matter in\nphytoplankton and thus is the major entry point of carbon into the oceanic biosphere. In addition to these, there are the\nenzymes that control CO2 production, NH4 excretion and the fluxes of phosphate. Some of these enzymes have been recognized\nand researched by marine scientists in the last thirty years. However, until recently the kinetic principles of enzyme\ncontrol have not been exploited to formulate accurate mathematical equations of the controlling physiological expressions.\nWere such expressions available they would increase our power to predict the rates of chemical transformations in the extracellular\nenvironment of microbial populations whether this extracellular environment is culture media or the ocean. Here we\nformulate from the principles of bisubstrate enzyme kinetics, mathematical expressions for the processes of NO3 reduction,\nO2 consumption, N2 fixation, total nitrogen uptake.