Nitrogenase catalyzes nitrogen fixation

Nitrogen fixation is the reduction of nitrogen gas. It proceeds by the stepwise addition of three pairs of hydrogen atoms to N2 (Figure 37.6). In addition to N2, these reactions require g

The enzyme nitrogenase binds a molecule of nitrogen gas.

Substrate: + 2H

Nitrogen gas (N2)

2| A reducing agent transfers three successive pairs of hydrogen atoms to N2.

three things:

37.6 Nitrogenase Fixes Nitrogen Throughout the chemical reactions of nitrogen fixation, the reactants are bound to the enzyme nitrogenase. A reducing agent transfers hydrogen atoms to nitrogen, and eventually the final product—ammonia—is released.

M The final products—two molecules of ammonia—are released, freeing the nitrogenase to bind another N2 molecule.

The enzyme nitrogenase binds a molecule of nitrogen gas.

2| A reducing agent transfers three successive pairs of hydrogen atoms to N2.

M The final products—two molecules of ammonia—are released, freeing the nitrogenase to bind another N2 molecule.

Substrate: + 2H

Nitrogen gas (N2)

Nitrogenase Nodules

Product:

Ammonia (NH3)

Nitrogenase

Binding of substrate

Product:

Ammonia (NH3)

Nitrogenase

Binding of substrate

Root hairs Cortical cells

Root hair

Root hairs Cortical cells

Root hair

Plant Root Bacteroid Nitrogenase

37.7 A Nodule Forms Rhizobium develops the ability to fix nitrogen only after entering a legume root.The diagrams show the sequence of events in nodule formation. The photograph shows bacteroids of Rhizobiumjaponicum in vesicles within a soybean root cell. A portion of an uninfected root cell is seen on the right.

Bacteroids

| The nodule forms from rapidly dividing, infected cortical cells.

37.7 A Nodule Forms Rhizobium develops the ability to fix nitrogen only after entering a legume root.The diagrams show the sequence of events in nodule formation. The photograph shows bacteroids of Rhizobiumjaponicum in vesicles within a soybean root cell. A portion of an uninfected root cell is seen on the right.

Bacteroids

| The nodule forms from rapidly dividing, infected cortical cells.

► a strong reducing agent to transfer hydrogen atoms to N2 and to the intermediate products of the reaction

► a great deal of energy, which is supplied by ATP

► the enzyme nitrogenase, which catalyzes the reaction

(Depending on the species of nitrogen fixer, either respiration or photosynthesis may provide both the necessary reducing agent and ATP.)

Nitrogenase is so strongly inhibited by oxygen that its presence in biochemical extracts was obscured and its discovery delayed because investigators had not thought to seek it under anaerobic conditions. It is therefore not surprising that many nitrogen fixers are anaerobes and live in environments with little or no O2. Because this crucial enzyme is so inhibited by O2, it was at first surprising that legumes respire aerobically, as do Rhizobium. Investigation of the root nodules where nitrogenase is found revealed how the enzyme could operate there.

Within a root nodule, O2 is maintained at a low level sufficient to support respiration, but not so high as to inactivate nitrogenase. The plant makes this possible by producing the protein leghemoglobin in the cytoplasm of the nodule cells. Leghemoglobin is a close relative of hemoglobin, the oxygen-carrying pigment of animals. Some plant nodules contain enough of it to be bright pink when viewed in cross section. Leghemoglobin, with its iron-containing heme groups, transports enough oxygen to the bacteroids to support their respiration.

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Responses

  • ANITA
    What chemical transformation is catalyzed by the enzyme nitrogenase?
    8 years ago
  • ensio
    What is the reducing agent for nitrogen fixation?
    8 years ago
  • maria
    What chemical transformations are catalyzed by the enzyme nitrogenase?
    8 years ago
  • prisco endrizzi
    What is nitrogenase enzyme in nodules?
    8 years ago
  • MICHAL
    What chemical transformations are catalyzed by the enzyme catalase, by nitrogenase?
    7 years ago
  • sven
    What enzyme catalyzes nitrogen fixation?
    6 years ago
  • zuzanna
    What is the enzyme substrate for nitrogen gas?
    6 years ago
  • michele
    What is bacteria catalyzed by nitrogenase?
    6 years ago
  • Facino
    What kind of chemical transformations are catalyzed by the enzyme nitrogenase?
    6 years ago
  • jesse
    What does the enzyme nitrogenase catalize?
    4 years ago
  • janne
    Which enzyme catalyzes the process of nitrogen fixation?
    4 years ago
  • milen
    What does the enzyme nitrogenase catalyze?
    3 years ago
  • ivan
    What kind of chemical reaction is catalyzed by nitrogenase in nitrogen fixing bacteria?
    3 years ago
  • BELLA
    What delayed the discovery of nitrogenase?
    2 years ago
  • adone
    How nitrogenase enzyme form nodule?
    2 years ago
  • Mackenzie
    What is the name of the enzyme that catalyzes nitrogen protein into ammonia?
    1 year ago

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