Behavior of respiratory metabolism and pyridine nucleotide levels in Oxyrrhis marina during starvation

Abstract

Respiration in eukaryotes is a physiological process that occurs wherever the oxygen and organic matter are present. Respiration is oxygen consumption (RO2) catalyzed by the respiratory electron transport system (ETS) enzymes. The physiological RO2 rate depends directly on the enzymatic control of the respiratory ETS activity. According to Packard et al. (1996), we argue that substrate availability is the most probable regulatory mechanism controlling this activity. The major ETS substrates are the pyridine nucleotides (PNs) and they occur as nicotine adenine dinucleotide (NAD) and as nicotine adenine dinucleotide phosphate (NADP). Up to now, no studies have quantified their intracellular concentrations in a marine dinoflagellate. Oxyrrhis marina is a microheterotrophic marine dinoflagellate which has been widely investigated. Nevertheless, no study has characterized its respiratory metabolism from measurements of oxygen consumption (RO2) and ETS activity. For this reason, our main objectives were 1) to measure RO2 and ETS activity in O. marina and to determine their behavior during starvation, and 2) to quantify the PN levels during the same period. To achieve these objectives, we fed O. marina ad libitum and then we monitored the ETS, RO2, protein and PN levels for 17 days.