amphibians, and aquatic and nonaquatic invertebrate
animals, and all such wild animals’ eggs, larvae, pupae,
orother immature stage and young.
feedback inhibition (end-product inhibition) A way
for the end product of a cell’s biosynthetic pathway to
stop the activity of the first enzymes in that pathway,
thereby controlling the enzymatic activity; it stops the
synthesis of the product.
female Sex classification by gender. The individual in
a sexually reproducing species that produces eggs.
Female mammals, for example, nourish their young with
milk. In humans, females have two X chromosomes.
FeMo-cofactor An inorganic CLUSTERthat is found
in the FeMo protein of the molybdenum-NITROGENASE
and is essential for the catalytic reduction of N 2 to
ammonia. This cluster contains Fe, Mo, and S in a
7:1:9 ratio. The structure of the COFACTORwithin the
FeMo protein can be described in terms of two
cuboidal SUBUNITs, Fe 4 S 3 and MoFe 3 S 3 bridged by
three S2–ions and “anchored” to the protein by a histi-
dine bound via an imidazole group to the Mo atom
and by a cysteine bound via a deprotonated SH group
to an Fe atom of the Fe 4 S 3 subunit. The Mo atom at
the periphery ofthe molecule is six-coordinate and, in
addition to the three sulfido LIGANDs and the histidine
imidazole, is also bound to two oxygen atoms from an
(R)-homocitrate molecule.
See alsoCOORDINATION.
Fenton reaction Fe2++ H 2 O 2 Fe3++ OH.+ OH–.
This is the iron-salt-dependent decomposition of dihy-
drogen peroxide, generating the highly reactive hydrox-
yl radical, possibly via an oxoiron(IV) intermediate.
Addition of a reducing agent such as ascorbate leads to
formation of an acyclic compound, which increases the
damage to biological molecules.
See alsoHABER-WEISS REACTION.
fermentation The anaerobic decomposition of com-
plex organic substances by microorganisms such as
bacteria, molds, or yeast, called ferments, on a fermen-
tation substrate that produce simpler substances or
some other desired effect, such as the yielding of
ethanol and carbon dioxide from yeast for commercial
purposes, the production of ATP and energy produc-
tion, and the development of antibiotics and enzymes.
Fermentation is used by microflora of the large intes-
tine to break down indigestible carbohydrates.
Large fermentors are used to culture microorgan-
isms for the production of some commercially valuable
products such as bread, beer, wine, and other beverages.ferredoxin A protein containing more than one iron
and ACID-LABILE SULFIDEthat displays electron-transfer
activity but not classical ENZYMEfunction.
See alsoHIPIP.ferriheme An iron(III) PORPHYRIN COORDINATION
complex.ferritin An iron storage protein consisting of a shell
of 24 protein SUBUNITs encapsulating up to 4,500 iron
atoms in the form of a hydrated iron(III) oxide.ferrochelatase An ENZYMEthat catalyzes the inser-
tion of iron into PROTOPORPHYRIN IXto formHEME.
The mammalian enzyme contains an IRON-SULFUR
CLUSTER.ferroheme An iron(II) PORPHYRIN COORDINATION
complex.ferromagnetic If there is coupling between the indi-
vidual magnetic dipole moments of a PARAMAGNETIC
sample, spontaneous ordering of the moments will
occur at low temperatures. If this ordering results in an
electronic ground state in which the moments are
aligned in the same direction (parallel), the substance is
said to be “ferromagnetic.” If the ordering results in an
electronic ground state in which the moments are
aligned in opposite directions, the substance is said to
be “antiferromagnetic.”126 feedback inhibition