Hepatic Production of 1,5‐Anhydrofructose and 1,5‐Anhydroglucitol in Rat by the third Glycogenolytic Pathway

A unique anhydrohexulose, 1,5‐anhydrofructose (1,5AnFru) has been detected in rat livers. Here we describe a microanalytical method for 1,5AnFru using GUMS and report results on the distribution and production of 1,5AnFru in rats. The highest levels of 1,5AnFru were found in the liver (0.43 μg/g wet tissue) and appreciable amounts were detected in adrenal gland and spleen (0.12 μg/g and 0.09 μg/g, respectively). Other organs contained lower amounts while plasma contained virtually no detectable 1,5AnFru. We also demonstrated that 1,5AnFru is produced in the cytosol fraction of rat liver homogenate when an α‐1,4‐glucan or glycogen was added; 1,5AnFru was readily reduced to 1,5‐anhydroglucitol with NADPH or at a reduced efficiency with NADH in the presence of a Mono Q chromatographic fraction obtained from the same cytosol preparation. Based on these results, we propose the existence of a third degradation pathway, in addition to the phosphorolytic and hydrolytic reaction sequences, from glycogen to 1,5–anhydroglucitol via 1,5AnFru in mammals. However, the physiological significance of 1,5AnFru and this putative minor glycogenolytic pathway in mammals remains obscure.