The vanadium effect in nitrogen fixation by azotobacter

Tungsten incorporation into Azotobacter vinelandii nitrogenase

“…The W-containing enzyme was inactive in all the reactions of the nitrate reductase complex except for its NADH-cytochrome c reductase activity [6, 71. In this report we show that W is incorporated into the nitrogenase complex of Azotobacter vinelandii. As we have found to be the case for v~adium [5], W is specifically associated with the Fe-MO protein fraction of nitrogenase. This W-containing protein fraction (Fe-W protein) is inactive in the acetylene reduction, hydrogen evolution, and reductant dependent ATPase activities of nitrogenase.…”

“…Our previous observations [S, 141 showed that when MO is present in excess in the growth medium it is taken up and, besides being incorporated into nitrogenase, is stored by Azotobacter in a protein bound form. Under MO starvation conditions essentially all available MO was found in the nitrogenase [5]. The high W concentrations might be accounted for by an unregulated uptake of the metal.…”

“…However, we can conclude that all three of the nitrogenase reactions are equally affected by the incorporation of W into the enzyme, suggesting a common active site. We have previously shown [5] that the nitrogenase substrate reduction activity is proportional to the molybdenum content of the enzyme, indicating that the active site contains a single MO. We suggest, from the results presented here, that this MO is also directly involved in the ATP hydrolysis and H2 evolution reactions of nitrogenase.…”

VANADIUM AS A TRACE ELEMENT IN THE BLUE‐GREEN ALGA, NOSTOC MUSCORUM: INFLUENCE ON NITROGENASE AND NITRATE REDUCTASE

“…Although there have been earlier reports of a V-nitrogenase {Burns, Fuchsman and Hardy, 1971) active in N2 fixation in A. vinelandii and A. chrococcum (Becking, 1962), and Clostridium butyricum (Jensen and Spencer, 1947), these require confirmation, because others are of the opinion that these bacteria still contained traces of Mo which were responsible for the nitrogenase activity (Benemann et al, 1972). The present results,too, emphasize that V is incapable of functionally replacing Mo, though it may increase Mo-protein binding in nitrogenase and nitrate reductase resulting in an increased N. and NOj" metabolism.…”

“…The effect of V at lower concentrations therefore, may he due to its involvement in stahilizing the Mo-protein hinding in nitrogenase and nitrate reductase. Earlier biochemical studies have shown that V influences the rate of Nj fixation in Azotobacter species by stabilizing Mo-protein binding in nitrogenase (Benemann et al, 1972). Although there have been earlier reports of a V-nitrogenase {Burns, Fuchsman and Hardy, 1971) active in N2 fixation in A.…”