On the relation between phosphate uptake and growth of the cyanobacterium Anacystis nidulans.

The energy dependent phosphate uptake by the cyanobacterium Anacystis nidulans has been analysed in terms of a "linear energy converter" that describes the interrelationship between phosphate incorporation into the polyphosphate pool and the photosynthetic proton flux at the thylakoid membrane. It is assumed that both processes are coupled in such a way that uptake proceeds with optimal efficiency at the prevailing phosphate concentration in the growth medium. On the basis of this model two important parameters of the uptake system can be calculated: first, a conductivity coefficient that reflects the activity of the uptake system and second, a minimal threshold value of external phosphate at which uptake ceases. The theoretical data are shown to fit the experimentally observed uptake behaviour of cyanobacteria when the same population is subjected to a transition from growth on low to high phosphate concentrations, mimicking a situation that frequently leads in natural waters to an algal bloom.

Isolation and functional reconstitution of a phosphate binding protein of the cyanobacterium Anacystis nidulans induced during phosphate-limited growth.

Adaptation of the blue-green algae Anacystis nidulans to phosphate-deficient growth leads to the expression of two membrane proteins, which appear as major constituents after separation by gel electrophoresis. One of these proteins, referred to as high affinity phosphate binding protein, has been isolated and its function reconstituted in liposomes. Partial sequencing showed no significant homologies to other proteins. The binding capacity of the proteoliposomes could be inhibited by arsenate but not by sulfhydryl reagents. Scatchard plot analyses of phosphate binding to reconstituted proteoliposomes suggested the existence of two different binding sites, one with a dissociation constant below micromolar and the other in the micromolar range.

Adaptive phosphate uptake behaviour of the cyanobacterium Anacystis nidulans: analysis by a proportional flow-force relation.

The phosphate uptake system of the cyanobacterium Anacystis nidulans has the capacity to store information about former fluctuations in the environmental phosphate concentration. Using nonequilibrium thermodynamics to characterize this phenomenon we show that information storage leads to the development of an extended range of validity over which there is a proportional relationship between uptake rate and the driving force of this process. The limits of this range reflect the extent of earlier fluctuations in the environmental phosphate concentration.

Characterization of the glutamate/aspartate-transport system in a symbiotic Nostoc sp.

The permeability properties of the cell membrane of a symbiotic Nostoc sp. for glutamate and aspartate were investigated. These compounds were translocated across the plasmalemma by a transport system which showed a very high affinity for glutamate and a lower one for aspartate. Since a concomitant release of glutamate was observed during the uptake of these two amino acids it is concluded that the transport proceeds via a counterexchange mechanism. In addition to this counterexchange a net release of glutamate occurred in the dark. Some aspects concerning the possible function of this transport system in the symbiotic association Geosiphon pyriforme are discussed.

The regulation of the energy-dependent phosphate uptake by the blue-green alga Anacystis nidulans.

Investigations of the energy-dependent accumulation of orthophosphate by the blue-green alga Anacystis nidulans have established: 1. The transport through the cell membrane is the rate-limiting step in the incorporation of phosphate.-2. This transport is facilitated by a "carrier" that can be activated by Ca(2+) and Mg(2+) and inhibited by EDTA.-3. The activation of the carrier in the light is associated with changes of the cytoplasmic Mg(2+) content.-4. Intracellular phosphate is shown to be present in bound form.-5. The energy-dependent accumulation of orthophosphate within the cell depends strictly on the cytoplasmic pH and not on the energy conversion at the thylakoid membrane which is responsible for the energy supply. The cytoplasmic pH is different in the light, in the dark, and in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Orthophosphate accumulation can most readily be explained in terms of a pH dependent precipitation into a complex with bivalent cations rather than by an active transport against a concentration gradient.

pH Changes in the Cytoplasm of the Blue-Green Alga Anacystis nidulans Caused by Light-dependent Proton Flux into the Thylakoid Space.

The pH in the cytoplasmic and thylakoid spaces of the blue-green alga, Anacystis nidulans, has been determined in the light and in the dark by uptake of 5,5-dimethyloxazolidine-2,4-dione and methylamine into the sucrose-impermeable (3)H-H(2)O space, as measured by silicon layer filtering centrifugation.Illumination causes an alkalinization in the cytoplasm which is accompanied by an acidification in the thylakoid space, reflecting light-dependent proton transport across the thylakoid membrane. Under light conditions, a pH gradient of approximately 2.8 between the cytoplasmic and thylakoid spaces has been measured that can be abolished almost completely by addition of the uncoupler, 3-chlorocarbonyl cyanide phenylhydrazone. The pH in the cytoplasm is independent of the pH in the medium.