Could somebody please enlighten me on the following problem:
Facts:
1) the _enzyme_ ferredoxin:nadph oxidoreductase (fnr) mediates the transfer of
electrons from the Fe-S centre of ferredoxin to the nicotinamide base of
nadp+
2) the _metalloprotein_ ferredoxin mediates the transfer of electrons
from the Fe-S centres FA/B to the FAD group of fnr
3) the _metalloprotein_ plastocyanin mediates the transfer of electrons
from the heme group of cytochrome f to the chlorophyll dimer P700
Question: When fnr, plastocyanin and ferredoxin are involved in catalysing
the process of oxidoreduction, and are not consumed in the process, why is
only fnr classified as an enzyme....?
My guess: plastocyanin and ferredoxin are electron transfer proteins, while
fnr is also involved in the transfer of H+. On the other hand, the definition
of an enzyme no longer seems to include the word _protein_ (ie. ribozymes) so
plastoquinone, which is a hydrogen/electron carrier might also fall under the
category enzyme.(?) Taking things to extremes, might the entire photosynthetic
electron transport apparatus not be defined as an H2O:NADP+ oxidoreductase..;-)
I would appreciate any help on this subject.
Harry
