Abstract
The ability to hydrolyze various fructose phosphates was studied by microscopic histochemical techniques. The liver cells and the tubular cells of the kidney split fructose 1,6-diphosphate, fructose 1-phosphate and fructose 6-phosphate, whereas only the vessels of the islets and exocrine pancreatic parenchyma showed a positive reaction with these substrates. Whether the splitting of fructose 1,6-diphosphate takes place at position 1 or 6 cannot be revealed by estimation of liberated phosphate. In samples prepared by Lowry's microtechniques, liberated fructose 6-phosphate was determined fluorometrically by measuring reduced nicotinamide adenine dinucleotide phosphate formation in coupled phosphoglucoisomerase and glucose 6-phosphate dehydrogenase reactions. The activity of hexose diphosphatase (EC 3.1.3.11) in the liver of the NZO mouse was in the same range (0.5-1 MKH) as that found in other species. Samples of both pancreatic islets and acini showed only insignificant activities which could be attributed to the nonspecific phosphatases present in the vessels. The absence of hexose diphosphatase in the endocrine cells of the islets suggests that these cells cannot reutilize triosephosphates in the pentose phosphate shunt or for gluconeogenesis.