Until now, the question of how arginine (Arg) biosynthesis operates in oxygenic
phototrophs at high salt concentrations has not been addressed experimentally.
This makes a green alga Dunaliella salina attractive for studying the molecular
events underlying the adjustment of Arg metabolism to high salinity. Enzyme assay
and Western blotting show that N-acetyl-L-glutamate kinase (NAGK) activity
decreases with increasing salinity and DsPII expression in cells is impaired.
Using GC-MS analysis, we also identified that the resulting levels of free Arg
are dependent on ornithine flux to putrescine and proline. These observations
suggest that NAGKs may have an alternative common PII-independent mode
of activation, raising important questions about the relationship between NAGK
control and the development of salinity tolerance during evolution.