title: Purification and Mn2+ activation of Rhodospirillum rubrum nitrogenase activating enzyme.
abstract: The Fe protein activating enzyme for Rhodospirillum rubrum nitrogenase was purified to approximately 90% homogeneity, using DE52-cellulose chromatography and sucrose density gradient centrifugation. Activating enzyme consists of a single polypeptide of molecular weight approximately 24,000. ATP was required for catalytic activity, but was relatively ineffective in the absence of Mg2+. When the concentration of MgATP2- was held in excess, there was an additional requirement for a free divalent metal ion (Mn2+) for enzyme activity. Kinetic experiments showed that the presence of Mg2+ influenced the apparent binding of Mn2+ by the enzyme, resulting in a lowering of the concentration of Mn2+ required to give half-maximum activity (K alpha) as the free Mg2+ concentration was increased. A low concentration of Mn2+ had a sparing effect on the requirement for free Mg2+. There is apparently a single metal-binding site on activating enzyme which preferentially binds Mn2+ as a positive effector, and free Mg2+ can compete for this site.
mesh_terms: D004789:Enzyme Activation; D004798:Enzymes / Q000302:isolation & purification / Q000378:metabolism*; D006026:Glycoside Hydrolases; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology*; D008970:Molecular Weight; D009699:N-Glycosyl Hydrolases; D012247:Rhodospirillum rubrum / Q000201:enzymology*
chemical_list: D004798:Enzymes; D008345:Manganese; D006026:Glycoside Hydrolases; D009699:N-Glycosyl Hydrolases; C036091:ADP-ribosyl-(dinitrogen reductase) hydrolase; D008274:Magnesium