CONSECUTIVE FORMATION OF SENSORY PHOTOSYSTEMS IN GROWING Halobacterium halobium

Abstract— The sensory photosystems PS 370 and PS 565 of Halobacierium halobium are actively degraded in the early growth phase and later resynthesized. Neither degradation nor resynthesis is correlated to the rate of cell division. The reappearance of photosensory activity requires de novo synthesis of proteins which are most likely directly involved in the sensory pathway. PS 370 appears earlier than PS 565 and thus may be studied independently of PS 565, before the latter is synthesized, or by blocking the synthesis of PS 565 with puromycin after PS 370 has appeared. The action spectrum of PS 370 alone shows the same maximum as the spectrum obtained when PS 565 is present. Carotenoids, which act as accessory pigments of PS 370, do not shift its activity peak. Also the maximum of PS 565 is not influenced by PS 370. We conclude that the maxima of the action spectra of PS 370 and PS 56.5 truely reflect the absorption maxima of the sensory retinal pigmentsP–370 andP–565.