NITROGENASE SYSTEM FROM AZOTOBACTER ACTIVATION ENERGY AND DIVALENT CATION REQUIREMENT

1. 1. The Arrhenius plot for nitrogenase from Azotobacter vinelandii is biphasic with an inflection at about 21°; the activation energy was calculated to be 14 600 cal/mole above this temperature and 39 000 cal/mole below. 2. 2. Values of 9 · 10-3 M and 3 · 10-4 M were determined for the Michaelis constants for hydrosulfite and for ATP, respetively, both above and below 21°. 3. 3. Mn2+, Co2+, Fe2+, and NI2+ (in that order of effectiveness) replaced Mg2+ in supporting nitrogenase activity; Cu2+ and Zn2+ were inhibitory, while Ca2+ was without effect. © 1969.