title: Calcium transport in membrane vesicles of Bacillus subtilis.
abstract: Right-side-out membrane vesicles of Bacillus subtilis W23 grown on tryptone-citrate medium accumulated Ca2+ under aerobic conditions in the presence of a suitable electron donor. Ca2+ uptake was an electrogenic process which was completely inhibited by carbonyl cyanide m-chlorophenylhydrazone or valinomycin and not by nigericin. This electrogenic uptake of calcium was strongly dependent on the presence of phosphate and magnesium ions. The system had a low affinity for Ca2+. The kinetic constants in membrane vesicles were Km = 310 microM Ca2+ and Vmax = 16 nmol/mg of protein per min. B. subtilis also possesses a Ca2+ extrusion system. Right-side-out-oriented membrane vesicles accumulated Ca2+ upon the artificial imposition of a pH-gradient, inside acid. This system had a high affinity for Ca2+; Km = 17 microM Ca2+ and Vmax = 3.3 nmol/mg of protein per min. Also, a membrane potential, inside positive, drove Ca2+ transport via this Ca2+ extrusion system. Evidence for a Ca2+ extrusion system was also supplied by studies of inside-out-oriented membrane vesicles in which Ca2+ uptake was energized by respiratory chain-linked oxidation of NADH or ascorbate-phenazine methosulfate. Both components of the proton motive force, the pH gradient and the membrane potential, drove Ca2+ transport via the Ca2+ extrusion system, indicating a proton-calcium antiport system with a H+ to Ca2+ stoichiometry larger than 2. The kinetic parameters of this Ca2+ extrusion system in inside-out-oriented membranes were Km = 25 microM and Vmax = 0.7 nmol/mg of protein per min.
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism; D001412:Bacillus subtilis / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002951:Citrates / Q000378:metabolism; D019343:Citric Acid; D004734:Energy Metabolism; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D008773:Methylphenazonium Methosulfate / Q000378:metabolism; D009243:NAD / Q000378:metabolism; D010101:Oxygen Consumption; D010710:Phosphates / Q000378:metabolism
chemical_list: D002951:Citrates; D010710:Phosphates; D009243:NAD; D019343:Citric Acid; D008773:Methylphenazonium Methosulfate; D008274:Magnesium; D001205:Ascorbic Acid; D002118:Calcium