From a chemical point of view, glucuronic acid
may be regarded as a derivative of glucose in which
the primary alcoholic group has been oxidised,
producing a carboxylic acid. The chemical properties of glucuronic acid have as yet been relatively little studied, but like all substances bearing
a potentially reducing aldehyde group, it will form
glycosides, and these 'conjugated' compounds,
without reducing properties, are known as
glucuronides.In living organisms, glucuronic acid is found
almost entirely in the conjugated form, and,
although very widely distributed, remarkably little
is known about its physiological function. As the
great importance of the compound can be inferred
from such widespread occurrence we may, before
considering the various theories regarding its
biosynthesis, briefly indicate the natural distribution of glucuronic acid.The work presented below was begun with the
intention of studying further the nature of glucuronide synthesis in the liver, using disintegrated
cell preparations (the so- called 'homogenates');
the use of such preparations is the next logical
step after slice experiments, for it enables more
consistent conditions to be attained, and prepares
for eventual enzyme isolation.In place of the overall results which are all
that can be ascertained from experiments on whole
animals, the homogenate technique offers a simple
and convenient method of directly demonstrating
definite reactions, such as the production of
o-aminophenylglucuronide on adding o-aminophenol.
Whereas with the intact animal, its perfused organ
or even slices of that organ, there is no certainty
that the added substance is really reaching the
responsible enzymes, or in what form or concentration
it might do so, in the homogenate technique a much
closer control can be exercised. The problems of
diffusibility of substrate and inhibitors through
the cell membrane, or of unequal tissue thicknesses
with their consequent metabolic differences, do not
exist in homogenates, where, provided reasonably
complete cell disruption has occurred, equal
volumes of the tissue preparation will behave
identically, being to the same degree exposed to
their environment. If the homogenate be used in
a sufficiently dilute form, autolysis will be checked
and by the addition of various metabolites and cofactors the enzyme system of part or all of the
desired reaction may be encouraged above the level
of others; subsequently the studied system may be
isolated from the crude homogenate and its behaviour
controlled to an extent impossible by any other
means.Therefore, since liver slices had already been
used by Storey to investigate the biosynthesis of
glucuronides, liver homogenates were employed in
the present work, which continues the study of
glucuronic acid conjugation in the liver.It was found during the course of this work
that appreciable glucuronide formation could be
obtained in liver homogenates, but only when a boiled liver extract was added to the medium
(Dutton & Storey, 1951). The bulk of this work,
then, concerns the isolation and purification of
the substance responsible, and the behaviour of
the enzyme system utilising it (Dutton & Storey,
1953).After the tabulation of the various standard
methods used, there follows a report of the experimental results, showing how, despite the trial of
many compounds of metabolic importance, no significant synthesis was obtained unless a boiled liver
extract containing the unknown factor was added.
Evidence that the products of synthesis were indeed
glucuronides is given, and a few observations on
the homogenate enzyme are appended. Work on the
nature of this synthesis with the crude factor is
then described, and the dissimilarity of the system
to that obtaining with sliced tissue (Storey, 1950)
pointed out. Lastly, the course of isolation and
purification of the factor is illustrated, with its
analysis and structural investigation. In the
Discussion the relationship of this work to the
results of previous investigators will be dealt
with, and its bearing on the wider aspects of
glucuronic acid metabolism indicated
