Some studies in the metabolism of laevulose

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.