BLUE AND RED LIGHT-DEPENDENT ALTERATIONS IN THE RATIO OF 2 FORMS OF GLUTAMINE-SYNTHETASE IN CHLORELLA-KESSLERI

Two forms of glutamine synthetase (EC 6.3.1.2) can be separated in cru de extracts of Chlorella kessleri on the basis of their different surf ace charges. The two enzyme forms (GS1 and GS2) respond differently up on transferring the cells from darkness to autotrophic growth in white light: the activity of GS2 increases, that of GS1 remains unchanged. The increase in GS2 activity is only brought about by blue light; in r ed light GS2 activity appears to be uninfluenced, while that of GS1 in creases. There are no indications of wavelength-dependent oligomerizat ion processes as a cause for the observed activity alterations. There is however, a strong influence of inhibitors of protein biosynthesis. Cycloheximide and lincomycin both affect the blue light-dependent incr ease in activity of GS2, cycloheximide preventing that of GS1 in red l ight completely. Since literature data point to localization of GS2 in the chloroplast, and GS1 in the cytosol, the data are discussed in vi ew of two different photoreceptors involved in the regulation of the a mounts of GS1 and GS2 in different compartments of the Chlorella cell.