Abstract
The high levels of δ-aminolevulinate synthetase (ALA-S) in Rhodopseudomonas palustris cells grown anaerobically in the light (Ph) decrease to those found in cells grown aerobically in the dark (A), when the former cultures were vigorously oxygenated; simultaneously bacteriochlorophyll (Bchl) synthesis abruptly halted leading to diminished steady-state specific Bchl content. When flushing oxygen was interrupted, enzymic activity increased, whether chloramphenicol was present or not in the medium; if the protein synthesis inhibitor was added when oxygenation started, ALA-S declined in the same fashion as in its absence, but thereafter reactivation of the enzyme was lower than before. Succinyl-CoA-synthetase and ALA-dehydratase activities were also measured under the conditions described, and no changes at all have been observed. The existence of different forms of ALA-S in R. palustris depending on growth conditions is postulated along with the formation of low molecular weight factors which can modulate ALA-S activity by binding to the enzyme; a widespread mechanism in the adaptation of micro-organisms to changes in environment. It is also proposed that this particular regulatory phenomenon, could be referred to as a switch off/on mechanism controlling ALA-S activity in R. palustris.
Highlights
The photosynthetic bacterium Rhodopseudomonas palustris can grow either anaerobically in the light developing an intracytoplasmatic membrane system and forming a variety of pigments, bacteriochlorophyll (Bchl) or aerobically in the dark; under these latter conditions Bchl synthesis is repressed'and the intracellular structures are absent (Viale et al, 1980)
One of the earliest responses associated to the adaptation from a photosynthetically grown culture to an aerobic atmosphere is a decrease in the activity of the first enzyme specific to porphyrin biosynthesis, 6-aminolevulinate synthetase (ALA-S)
In previous papers (Viale et al, 1980b, 1986) we have reported evidence on the existence of low molecular weight factors, which would modulate the activity of ALA-S in R. palustris
Summary
The photosynthetic bacterium Rhodopseudomonas palustris can grow either anaerobically in the light developing an intracytoplasmatic membrane system and forming a variety of pigments, bacteriochlorophyll (Bchl) or aerobically in the dark; under these latter conditions Bchl synthesis is repressed'and the intracellular structures are absent (Viale et al, 1980). The levels of ALA-S in aerobic (A) cells are about half of those in photosynthetically (Ph) cells This is indicating that this enzyme plays an important role in the control of Bchl synthesis. Under aerobic conditions a factor is formed which can increase basic enzyme activity when able to bind it.
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