title: Porphyrin biosynthesis in Rhodopseudomonas palustris--XII. delta-Aminolevulinate synthetase switch-off/on regulation.
abstract: The high levels of delta-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.
mesh_terms: D000624:5-Aminolevulinate Synthetase / Q000378:metabolism*; D000222:Adaptation, Physiological; D001429:Bacteriochlorophylls / Q000096:biosynthesis; D002701:Chloramphenicol / Q000494:pharmacology; D006706:Homeostasis; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000096:biosynthesis*; D012241:Rhodopseudomonas / Q000201:enzymology*
chemical_list: D001429:Bacteriochlorophylls; D011166:Porphyrins; D002701:Chloramphenicol; D000624:5-Aminolevulinate Synthetase