Abstract
Glutamine synthetase plays a key role in nitrogen metabolism, thus the fine regulation of this enzyme in Prochlorococcus, which is especially important in the oligotrophic oceans where this marine cyanobacterium thrives. In this work, we studied the metal-catalyzed oxidation of glutamine synthetase in cultures of Prochlorococcus marinus strain PCC 9511 subjected to nutrient limitation. Nitrogen deprivation caused glutamine synthetase to be more sensitive to metal-catalyzed oxidation (a 36% increase compared to control, non starved samples). Nutrient starvation induced also a clear increase (three-fold in the case of nitrogen) in the concentration of carbonyl derivatives in cell extracts, which was also higher (22%) upon addition of the inhibitor of electron transport, DCMU, to cultures. Our results indicate that nutrient limitations, representative of the natural conditions in the Prochlorococcus habitat, affect the response of glutamine synthetase to oxidative inactivating systems. Implications of these results on the regulation of glutamine synthetase by oxidative alteration prior to degradation of the enzyme in Prochlorococcus are discussed.
Highlights
Prochlorococcus is a marine cyanobacterium responsible for an important part of the primary production in the intertropical oceans where it is the dominant photosynthetic organism [1,2,3,4]
In order to study whether metal-catalyzed oxidation (MCO) promotes the carbonylation of the GS from Prochlorococcus, cell extracts were incubated in the presence of two inactivating systems that promote the formation of reactive oxygen species: NADH/Fe3+ and ascorbate/Cu2+; the inactivating effects of both systems have been previously described [15]
The carbonylated proteins increased in the samples exposed to the MCO systems, while in the control samples no bands were detected in our experiments (Fig 1)
Summary
Prochlorococcus is a marine cyanobacterium responsible for an important part of the primary production in the intertropical oceans where it is the dominant photosynthetic organism [1,2,3,4]. Its ability to cope with the oligotrophic conditions in its natural habitat is a critical part of its life strategy [4,5,6,7,8,9] and studying nutrient assimilation is crucial to understand the success of Prochlorococcus in the ocean. Nitrogen is the most important nutrient controlling primary productivity in the marine environment, together with iron and phosphorus [10]. The preferred nitrogen source for all the Prochlorococcus strains studied so far is ammonium [11, 12] and the glutamine synthetase/.
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