Abstract
The extensive use of sucrose in everyday
life and the increasing popularity of the laevulose
tolerance test as a test of liver function
necessitates a more comprehensive knowledge of the
metabolism of laevulose. The earlier workers in this
field were handicapped by only having slow and
unreliable methods for the estimation of laevulose,
but recently rapid and reliable methods have been
evolved.
The hypothesis that the metabolism of laevulose
consists essentially in its conversion to glucose,
after which its metabolism is identical with the
latter sugar, is unable to account for certain
characteristics, and these cannot be explained as
due to differences in the rate of absorption of the
two sugars and the speed with which laevulose
becomes available as glucose. For example, the
rate of glycogen deposition after fructose ingestionis greater that with glucose, the speed of
oxidation of laevulose as judged by its specific
dynamic action and its effect on the R.Q is out of
line with its rate of conversion to glucose,and
glucose is less effective than laevulose in
preventing and relieving ketosis. These facts lead
to the enquiry whether oxidation or glycogen
formation may not precede glucose formation.
Glucose is always considered the physiological
sugar because it is found in blood and is the final
product in the enzymic and acid hydrolyses of
glycogen. However, laevulose must also be classed
as a physiological sugar because of its ready
isolation as fructose diphosphate.
