molybdenum cofactor(Moco) The molybdenum
complex of the MOLYBDOPTERIN PROSTHETIC GROUP
(LIGAND). In the molybdenum COFACTOR, the minimal
COORDINATIONof the Mo atom is thought to be pro-
vided by the chelating dithiolenato group of the molyb-
dopterin and either two oxo or one oxo and one
sulfido ligands.
molybdopterin The PROSTHETIC GROUP associated
with the Mo atom of the MOLYBDENUM COFACTOR
found in all molybdenum-containing ENZYMEs except
NITROGENASE. Many of the enzymes catalyze two-elec-
tron redox reactions that involve the net exchange of
an oxygen atom between SUBSTRATEand water. The
molybdopterin prosthetic group contains a pterin ring
bound to a dithiolene functional group on the 6-alkyl
side chain. In bacterial enzymes a NUCLEOTIDE is
attached to the phosphate group.
monoamine Small organic molecule containing both
a carboxyl group and an amino group bonded to the
same carbon atom, e.g., histamine, serotonin,
epinephrine, and norepinephrine.
monomer A basic building block or small organic
molecule that makes up a polymer when combined
with identical or similar monomers through polymer-
ization. Polymers are important substances in organ-
isms, e.g., proteins are polymers.monooxygenase An ENZYME that catalyzes the
INSERTIONof one atom of oxygen, derived from O 2 ,
into an aromatic or aliphatic compound. The reaction
is coupled to the oxidation of a coSUBSTRATEsuch as
NAD(P)H or 2-oxoglutarate.monoprotic acid An acid that can donate one H+.
Hydrochloric acid (HCl) is an example.monosaccharide A simple sugar such as fructose or
glucose that cannot be decomposed by hydrolysis; color-
less crystalline substances with a sweet taste that have
the same general formula, CnH 2 nOn. They are classified
by size according to the number of carbon atoms in the
chain such as dioses, two carbon-ring backbone; trioses,
three carbon-ring backbone; heptose, with seven carbon-
ring backbone, etc.; further classified as aldoses (when
carbonyl group is an aldehyde) or ketoses (contains a
carbonyl [keto] group in its straight-chain form).morphogen A diffusible protein molecule present in
embryonic tissues that, through a concentration gradient,
can influence the development process of a cell; different
morphogen concentrations specify different cell fates.morphometrics A branch of mathematics that
focuses on the study of the metrical and statistical
properties of shapes and the changes of geometric
objects both organic or inorganic. Biologically relevant
when dealing with species that have morphs that
appear radically different.Mössbauer effect Resonance absorption of gamma
radiation by specific nuclei arranged in a crystal lattice
in such a way that the recoil momentum is shared by
many atoms. It is the basis of a form of spectroscopy
used for studying coordinated metal ions. The principal
application in bioinorganic chemistry is^57 Fe. The
parameters derived from the Mössbauer spectrum (iso-
mer shift, quadrupole splitting, and the HYPERFINEcou-Mössbauer effect 187