Kinetic studies of nitrogenase from soya-bean root-nodule bacteroids.
The apparent Michaelis constants [K'(N(2)) and K'(C(2)H(2))] and the corresponding apparent maximum velocity values (V') for soya-bean bacteroid nitrogenase increased concomitantly in response to increases in nitrogenase Fe-protein concentration and ATP concentration in cell-free assays and in response to O(2) pressure in intact nodules and bacteroid suspensions. K'(C(2)H(2)) in cell-free assays was also affected by pH and by Na(2)S(2)O(4) concentration. Nitrogenase Fe-protein behaved as a catalytic effector reacting at interacting sites on the nitrogenase Fe-Mo-protein. The results indicated that the Fe-Mo-protein probably bears the catalytic sites for N(2) and C(2)H(2) reduction. It is concluded that reduction of N(2) or C(2)H(2) by this nitrogenase involves a reaction mechanism with a sequence of unknown order. The sequence in which substrate, enzyme, effector, ATP and reductant react determines which of the various rate-constants are involved in the apparent Michaelis constant, whose true kinetic meaning was thus unresolved.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000693:Anaerobiosis; D001439:Bacteroides / Q000187:drug effects / Q000201:enzymology*; D001665:Binding Sites; D002850:Chromatography, Gel; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation; D006863:Hydrogen-Ion Concentration; D007501:Iron; D007700:Kinetics; D008433:Mathematics; D008954:Models, Biological; D008982:Molybdenum; D009584:Nitrogen; D009586:Nitrogen Fixation; D009587:Nitrogen Isotopes; D010088:Oxidoreductases / Q000378:metabolism*; D010100:Oxygen; D010944:Plants; D011485:Protein Binding; D013025:Glycine max; D013885:Thiosulfates / Q000494:pharmacology
D009587:Nitrogen Isotopes; D013885:Thiosulfates; D008982:Molybdenum; D000255:Adenosine Triphosphate; D007501:Iron; D010088:Oxidoreductases; D009584:Nitrogen; D010100:Oxygen; D004229:Dithiothreitol