title: Uptake of protoporphyrin and continuous spectrophotometric assay for magnesium chelatase in Rhodobacter spheroides.
abstract: Uptake of protoporphyrin was shown by Rhodobacter spheroides under anaerobic conditions in the dark. The process was not energy-dependent but required EGTA and was markedly stimulated by Methyl Viologen. Kinetic studies were consistent with a saturable process with Kd = 5-10 microM and Bmax. = 2.2 nmol of protoporphyrin bound/mg dry weight of cells. Bound protoporphyrin could be converted into magnesium protoporphyrin monomethyl ester under anaerobic conditions in the light or at low pO2 (6.3%) in the dark. This formed the basis of a sensitive continuous spectrophotometric assay for magnesium chelatase, which avoids the need to extract the product into organic solvent, and may facilitate the development of a cell-free system for magnesium chelatase in photosynthetic bacteria. It is proposed also that the uptake mechanism shown for exogenous protoporphyrin may indicate the existence of a ligand or carrier system for endogenously produced protoporphyrin essential for magnesium chelatase activity.
authors.affiliation: Department of Clinical Pharmacology and Therapeutics, St Mary's Hospital Medical School, Imperial College of Science, Technology and Medicine, Paddington, London, U.K.
authors.forename: A
authors.initials: A
authors.lastname: Gorchein
mesh_terms: D004533:Egtazic Acid; D007700:Kinetics; D008190:Lyases / Q000378:metabolism*; D010269:Paraquat; D011524:Protoporphyrins / Q000378:metabolism*; D012242:Rhodobacter sphaeroides / Q000201:enzymology*; D013057:Spectrum Analysis
chemical_list: D011524:Protoporphyrins; D004533:Egtazic Acid; D008190:Lyases; C086788:magnesium chelatase; D010269:Paraquat