A B S T R A C T The enzyme activities involved in fructose metabolism were measured in samples of human liver. On the basis of U/g of wet-weight the following results were found: ketohexokinase, glycerol kinase, 0.62. Sorbitol dehydrogenases (25.0 U/g), hexosediphosphatase (4.06 U/g), hexokinase (0.23 U/g), and glucokinase (0.08 U/g) were also measured. Comparing these results with those of the rat liver it becomes clear that the activities of alcohol dehydrogenases (NAD and NADP) in rat liver are higher than those in human liver, and that the values of ketohexokinase, sorbitol dehydrogenases, and hexosediphosphatase in human liver are lower than those values found in rat liver. Human liver contains only traces of glycerate kinase.The rate of fructose uptake from the blood, as described by other investigators, can be based on the activity of ketohexokinase reported in the present paper. In human liver, ketohexokinase is present in a four-fold activity of glucokinase and Requests for reprints should be addressed to Dr.

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Aldehyde dehydrogenase from bovine liver has been purified to homogeneity. Amino acid composition showed a high content of cysteine of 32 mol/mol enzyme. The enzyme is composed of four identical subunits as judged by sodium dodecyl sulfate gel electrophoresis and end‐group analysis. The molecular weight was determined to be 220 000 ± 10 000 by sedimentation equilibrium analysis in an analytical ultracentrifuge. The Michaelis constants for NAD+, glyceraldehyde and acetaldehyde were found to be 47 μM, 170 μM and 130 μM, respectively.