Enzyme des Fructosestoffwechsels. Aktivität und Verteilung in der Leber der Ratte

Abstract

The activities of enzymes involved in fructose metabolism were determined in rat liver. Their distribution within the cell was measured. New methods are reported for the determination of aldehyde dehydrogenase and triokinase. A simple method is described for the quantitative determination of enzyme activities in the cytoplasm and mitochondria of liver cells. Ketohexokinase, ketose-1-phosphate aldolase, triokinase and hexose diphosphatase were found only in the cytoplasm. Aldehyde dehydrogenase, D-glycerate kinase and the sorbitol dehydrogenases were found both in the cytoplasm and the mitochondria. A physiological reduction of D-glyceraldehyde to glycerol, followed by phosphorylation to L-glycerol-3-phosphate seems improbable from kinetic measurements. Alcohol dehydrogenase and glycerol kinase are confined to the cytoplasm. The possibility that D-glyceraldehyde is metabolized in or on the surface of the mitochondria is discussed. A comparison of the activities of hexokinase and ketohexokinase shows that, under optimal conditions, more fructose than glucose can be metabolized in the liver.