ALTERATIONS IN THE RATIO OF 2 FORMS OF GLUTAMINE-SYNTHETASE IN CHLORELLA-KESSLERI - EFFECTS OF BLUE-LIGHT AND RED-LIGHT AND OF EXOGENOUS NITROGEN SUPPLY

In crude extracts of Chlorella kessleri, two forms of glutamine synthe tase (EC 6.3.1.2) can be separated by their different surface charges. From literature data, one of them, GS1, is considered to reside in th e cytosol, and the other one, GS2, to be located in the chloroplast. B oth enzyme forms are separately influenced by light and by nitrate sup ply: In the presence of nitrate in the culture medium (under growth co nditions), GS1 activity is higher but GS2 activity is lower in extract s of red light-grown cells than in those of blue light grown cells. In extracts of white light-grown cells GS1 and GS2 activities resemble t hose of extracts of blue light-grown cells. At nitrate deficiency GS2 activity is hardly detectable in extracts of algae from white light co nditions while GS1 activity is very high. Resupply of nitrate leads to an increase of GS2 only in the presence of blue light. The involvemen t of two different photoreceptors in the regulation of the amounts of GS1 and GS2 of Chlorella is discussed.