Some of the cytochrome b6 f complexes are found in the stroma region of the membrane, where photosystem I is located. Under certain conditions cyclic electron flow from the reducing side of photosystem I, through the b6 f complex and back to P700, is known to occur.

TLS Online TPP Program

#Id: 9266

#Unit 6. System Physiology – Plant

N2 constitutes about 80% of the earth’s atmosphere, but the stability of its triple bond renders it inert and metabolically inaccessible to most organisms.

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#Id: 9267

#Unit 6. System Physiology – Plant

Diazotrophs are able to catalyze the enzymatic reduction of this compound to ammonia (NH3) using the enzyme nitrogenase

TLS Online TPP Program

#Id: 9268

#Unit 6. System Physiology – Plant

Nitrogenase is a complex consisting of the MoFe protein (dinitrogenase or component I) a heterotetramer, and the Fe protein (dinitrogenase reductase or component II) a homodimer.

TLS Online TPP Program

#Id: 9269

#Unit 6. System Physiology – Plant

Fe protein 

contains 2 identical subunits (dimer) – nif H

Each subunit has MW of 30 ~ 72 kD.

Each subunit contains an Fe-S cluster (4Fe and 4S2-).

TLS Online TPP Program

#Id: 9270

#Unit 6. System Physiology – Plant

MoFe protein 

2 pairs of identical subunits (tetramer, nif D & nif K)

A total of MW 180 ~ 235kD

Each subunit has 2 Mo-Fe-S clusters.

Both Fe proteins and MoFe proteins are sensitive to O2. 

TLS Online TPP Program

#Id: 9271

#Unit 6. System Physiology – Plant